Set Array Size In Pl/Sql What Is The Assignment Operator

5 PL/SQL Collections and Records

A composite data type stores values that have internal components. You can pass entire composite variables to subprograms as parameters, and you can access internal components of composite variables individually. Internal components can be either scalar or composite. You can use scalar components wherever you can use scalar variables. PL/SQL lets you define two kinds of composite data types, collection and record. You can use composite components wherever you can use composite variables of the same type.

Note:

If you pass a composite variable as a parameter to a remote subprogram, then you must create a redundant loop-back , so that when the remote subprogram compiles, the type checker that verifies the source uses the same definition of the user-defined composite variable type as the invoker uses. For information about the statement, see Oracle Database SQL Language Reference.

In a collection, the internal components always have the same data type, and are called elements. You can access each element of a collection variable by its unique index, with this syntax: . To create a collection variable, you either define a collection type and then create a variable of that type or use .

In a record, the internal components can have different data types, and are called fields. You can access each field of a record variable by its name, with this syntax: . To create a record variable, you either define a type and then create a variable of that type or use or .

You can create a collection of records, and a record that contains collections.

Collection Topics

Record Topics

Note:

Several examples in this chapter define procedures that print their composite variables. Several of those procedures invoke this standalone procedure, which prints either its integer parameter (if it is not ) or the string : CREATE OR REPLACE PROCEDURE print (n INTEGER) IS BEGIN IF n IS NOT NULL THEN DBMS_OUTPUT.PUT_LINE(n); ELSE DBMS_OUTPUT.PUT_LINE('NULL'); END IF; END print; /

Some examples in this chapter define functions that return values of composite types.

You can understand the examples in this chapter without completely understanding PL/SQL procedures and functions, which are explained in Chapter 8, "PL/SQL Subprograms".

Collection Types

PL/SQL has three collection types—associative array, (variable-size array), and nested table. Table 5-1 summarizes their similarities and differences.

Table 5-1 PL/SQL Collection Types

Collection TypeNumber of Elements
Index TypeDense or Sparse
Uninitialized Status
Where Defined
Can Be ADT Attribute Data Type

Associative array (or index-by table)

Unspecified

String or

Either

Empty

In PL/SQL block or package

No

(variable-size array)

Specified

Integer

Always dense

Null

In PL/SQL block or package or at schema level

Only if defined at schema level

Nested table

Unspecified

Integer

Starts dense, can become sparse

Null

In PL/SQL block or package or at schema level

Only if defined at schema level


Number of Elements

If the number of elements is specified, it is the maximum number of elements in the collection. If the number of elements is unspecified, the maximum number of elements in the collection is the upper limit of the index type.

Dense or Sparse

A dense collection has no gaps between elements—every element between the first and last element is defined and has a value (the value can be unless the element has a constraint). A sparse collection has gaps between elements.

Uninitialized Status

An empty collection exists but has no elements. To add elements to an empty collection, invoke the method (described in "EXTEND Collection Method").

A null collection (also called an atomically null collection) does not exist. To change a null collection to an existing collection, you must initialize it, either by making it empty or by assigning a non- value to it (for details, see "Collection Constructors" and "Assigning Values to Collection Variables"). You cannot use the method to initialize a null collection.

Where Defined

A collection type defined in a PL/SQL block is a local type. It is available only in the block, and is stored in the database only if the block is in a standalone or package subprogram. (Standalone and package subprograms are explained in "Nested, Package, and Standalone Subprograms".)

A collection type defined in a package specification is a public item. You can reference it from outside the package by qualifying it with the package name (). It is stored in the database until you drop the package. (Packages are explained in Chapter 10, "PL/SQL Packages.")

A collection type defined at schema level is a standalone type. You create it with the "CREATE TYPE Statement". It is stored in the database until you drop it with the "DROP TYPE Statement".

Note:

A collection type defined in a package specification is incompatible with an identically defined local or standalone collection type (see Example 5-31 and Example 5-32).

Can Be ADT Attribute Data Type

To be an ADT attribute data type, a collection type must be a standalone collection type. For other restrictions, see Restrictions on datatype.

Translating Non-PL/SQL Composite Types to PL/SQL Composite Types

If you have code or business logic that uses another language, you can usually translate the array and set types of that language directly to PL/SQL collection types. For example:

Non-PL/SQL Composite TypeEquivalent PL/SQL Composite Type
Hash tableAssociative array
Unordered tableAssociative array
SetNested table
BagNested table
Array

See Also:

Oracle Database SQL Language Reference for information about the function, which converts one SQL data type or collection-typed value into another SQL data type or collection-typed value.

Associative Arrays

An associative array (formerly called PL/SQL table or index-by table) is a set of key-value pairs. Each key is a unique index, used to locate the associated value with the syntax .

The data type of can be either a string type or . Indexes are stored in sort order, not creation order. For string types, sort order is determined by the initialization parameters and .

Like a database table, an associative array:

  • Is empty (but not null) until you populate it

  • Can hold an unspecified number of elements, which you can access without knowing their positions

Unlike a database table, an associative array:

  • Does not need disk space or network operations

  • Cannot be manipulated with DML statements

Example 5-1 defines a type of associative array indexed by string, declares a variable of that type, populates the variable with three elements, changes the value of one element, and prints the values (in sort order, not creation order). ( and are collection methods, described in "Collection Methods".)

Example 5-1 Associative Array Indexed by String

DECLARE -- Associative array indexed by string: TYPE population IS TABLE OF NUMBER -- Associative array type INDEX BY VARCHAR2(64); -- indexed by string city_population population; -- Associative array variable i VARCHAR2(64); -- Scalar variable BEGIN -- Add elements (key-value pairs) to associative array: city_population('Smallville') := 2000; city_population('Midland') := 750000; city_population('Megalopolis') := 1000000; -- Change value associated with key 'Smallville': city_population('Smallville') := 2001; -- Print associative array: i := city_population.FIRST; -- Get first element of array WHILE i IS NOT NULL LOOP DBMS_Output.PUT_LINE ('Population of ' || i || ' is ' || city_population(i)); i := city_population.NEXT(i); -- Get next element of array END LOOP; END; /

Result:

Population of Megalopolis is 1000000 Population of Midland is 750000 Population of Smallville is 2001

Example 5-2 defines a type of associative array indexed by and a function that returns an associative array of that type.

Example 5-2 Function Returns Associative Array Indexed by PLS_INTEGER

DECLARE TYPE sum_multiples IS TABLE OF PLS_INTEGER INDEX BY PLS_INTEGER; n PLS_INTEGER := 5; -- number of multiples to sum for display sn PLS_INTEGER := 10; -- number of multiples to sum m PLS_INTEGER := 3; -- multiple FUNCTION get_sum_multiples ( multiple IN PLS_INTEGER, num IN PLS_INTEGER ) RETURN sum_multiples IS s sum_multiples; BEGIN FOR i IN 1..num LOOP s(i) := multiple * ((i * (i + 1)) / 2); -- sum of multiples END LOOP; RETURN s; END get_sum_multiples; BEGIN DBMS_OUTPUT.PUT_LINE ( 'Sum of the first ' || TO_CHAR(n) || ' multiples of ' || TO_CHAR(m) || ' is ' || TO_CHAR(get_sum_multiples (m, sn)(n)) ); END; /

Result:

Sum of the first 5 multiples of 3 is 45

Topics

Declaring Associative Array Constants

When declaring an associative array constant, you must create a function that populates the associative array with its initial value and then invoke the function in the constant declaration, as in Example 5-3. (The function does for the associative array what a constructor does for a varray or nested table. For information about constructors, see "Collection Constructors".)

Example 5-3 Declaring Associative Array Constant

CREATE OR REPLACE PACKAGE My_Types AUTHID DEFINER IS TYPE My_AA IS TABLE OF VARCHAR2(20) INDEX BY PLS_INTEGER; FUNCTION Init_My_AA RETURN My_AA; END My_Types; / CREATE OR REPLACE PACKAGE BODY My_Types IS FUNCTION Init_My_AA RETURN My_AA ISRet My_AA;BEGINRet(-10) := '-ten';Ret(0) := 'zero';Ret(1) := 'one';Ret(2) := 'two';Ret(3) := 'three';Ret(4) := 'four';Ret(9) := 'nine';RETURN Ret;END Init_My_AA; END My_Types; / DECLARE v CONSTANT My_Types.My_AA := My_Types.Init_My_AA(); BEGIN DECLARE Idx PLS_INTEGER := v.FIRST(); BEGIN WHILE Idx IS NOT NULL LOOP DBMS_OUTPUT.PUT_LINE(TO_CHAR(Idx, '999')||LPAD(v(Idx), 7)); Idx := v.NEXT(Idx); END LOOP; END; END; /

Result:

-10 -ten 0 zero 1 one 2 two 3 three 4 four 9 nine PL/SQL procedure successfully completed.

NLS Parameter Values Affect Associative Arrays Indexed by String

National Language Support (NLS) parameters such as , , and affect associative arrays indexed by string.

Topics

Changing NLS Parameter Values After Populating Associative Arrays

The initialization parameters and determine the storage order of string indexes of an associative array. If you change the value of either parameter after populating an associative array indexed by string, then the collection methods , , , and (described in "Collection Methods") might return unexpected values or raise exceptions. If you must change these parameter values during your session, restore their original values before operating on associative arrays indexed by string.

Indexes of Data Types Other Than VARCHAR2

In the declaration of an associative array indexed by string, the string type must be or one of its subtypes. However, you can populate the associative array with indexes of any data type that the function can convert to . (For information about , see Oracle Database SQL Language Reference.)

If your indexes have data types other than and its subtypes, ensure that these indexes remain consistent and unique if the values of initialization parameters change. For example:

  • Do not use as an index.

    If the value of changes, then the value of might also change.

  • Do not use different indexes that might be converted to the same value.

  • Do not use or indexes that differ only in case, accented characters, or punctuation characters.

    If the value of ends in (case-insensitive comparisons) or (accent- and case-insensitive comparisons), then indexes that differ only in case, accented characters, or punctuation characters might be converted to the same value.

Passing Associative Arrays to Remote Databases

If you pass an associative array as a parameter to a remote database, and the local and the remote databases have different or values, then:

  • The collection method , , or (described in "Collection Methods") might return unexpected values or raise exceptions.

  • Indexes that are unique on the local database might not be unique on the remote database, raising the predefined exception .

Appropriate Uses for Associative Arrays

An associative array is appropriate for:

  • A relatively small lookup table, which can be constructed in memory each time you invoke the subprogram or initialize the package that declares it

  • Passing collections to and from the database server

    Declare formal subprogram parameters of associative array types. With Oracle Call Interface (OCI) or an Oracle precompiler, bind the host arrays to the corresponding actual parameters. PL/SQL automatically converts between host arrays and associative arrays indexed by .

    Note:

    You cannot declare an associative array type at schema level. Therefore, to pass an associative array variable as a parameter to a standalone subprogram, you must declare the type of that variable in a package specification. Doing so makes the type available to both the invoked subprogram (which declares a formal parameter of that type) and the invoking subprogram or anonymous block (which declares and passes the variable of that type). See Example 10-2.

    Tip:

    The most efficient way to pass collections to and from the database server is to use associative arrays with the statement or clause. For details, see "FORALL Statement" and "BULK COLLECT Clause".

An associative array is intended for temporary data storage. To make an associative array persistent for the life of a database session, declare it in a package specification and populate it in the package body.

Varrays (Variable-Size Arrays)

A varray (variable-size array) is an array whose number of elements can vary from zero (empty) to the declared maximum size. To access an element of a varray variable, use the syntax . The lower bound of is 1; the upper bound is the current number of elements. The upper bound changes as you add or delete elements, but it cannot exceed the maximum size. When you store and retrieve a varray from the database, its indexes and element order remain stable.

Figure 5-1shows a varray variable named , which has maximum size 10 and contains seven elements. () references the nth element of . The upper bound of is 7, and it cannot exceed 10.

The database stores a varray variable as a single object. If a varray variable is less than 4 KB, it resides inside the table of which it is a column; otherwise, it resides outside the table but in the same tablespace.

An uninitialized varray variable is a null collection. You must initialize it, either by making it empty or by assigning a non- value to it. For details, see "Collection Constructors" and "Assigning Values to Collection Variables".

Example 5-4 defines a local type, declares a variable of that type (initializing it with a constructor), and defines a procedure that prints the varray. The example invokes the procedure three times: After initializing the variable, after changing the values of two elements individually, and after using a constructor to the change the values of all elements. (For an example of a procedure that prints a varray that might be null or empty, see Example 5-24.)

Example 5-4 Varray (Variable-Size Array)

DECLARE TYPE Foursome IS VARRAY(4) OF VARCHAR2(15); -- VARRAY type -- varray variable initialized with constructor: team Foursome := Foursome('John', 'Mary', 'Alberto', 'Juanita'); PROCEDURE print_team (heading VARCHAR2) IS BEGIN DBMS_OUTPUT.PUT_LINE(heading); FOR i IN 1..4 LOOP DBMS_OUTPUT.PUT_LINE(i || '.' || team(i)); END LOOP; DBMS_OUTPUT.PUT_LINE('---'); END; BEGIN print_team('2001 Team:'); team(3) := 'Pierre'; -- Change values of two elements team(4) := 'Yvonne'; print_team('2005 Team:'); -- Invoke constructor to assign new values to varray variable: team := Foursome('Arun', 'Amitha', 'Allan', 'Mae'); print_team('2009 Team:'); END; /

Result:

2001 Team: 1.John 2.Mary 3.Alberto 4.Juanita --- 2005 Team: 1.John 2.Mary 3.Pierre 4.Yvonne --- 2009 Team: 1.Arun 2.Amitha 3.Allan 4.Mae ---

Topics

Appropriate Uses for Varrays

A varray is appropriate when:

  • You know the maximum number of elements.

  • You usually access the elements sequentially.

Because you must store or retrieve all elements at the same time, a varray might be impractical for large numbers of elements.

Nested Tables

In the database, a nested table is a column type that stores an unspecified number of rows in no particular order. When you retrieve a nested table value from the database into a PL/SQL nested table variable, PL/SQL gives the rows consecutive indexes, starting at 1. Using these indexes, you can access the individual rows of the nested table variable. The syntax is . The indexes and row order of a nested table might not remain stable as you store and retrieve the nested table from the database.

The amount of memory that a nested table variable occupies can increase or decrease dynamically, as you add or delete elements.

An uninitialized nested table variable is a null collection. You must initialize it, either by making it empty or by assigning a non- value to it. For details, see "Collection Constructors" and "Assigning Values to Collection Variables".

Example 5-5 defines a local nested table type, declares a variable of that type (initializing it with a constructor), and defines a procedure that prints the nested table. (The procedure uses the collection methods and , described in "Collection Methods".) The example invokes the procedure three times: After initializing the variable, after changing the value of one element, and after using a constructor to the change the values of all elements. After the second constructor invocation, the nested table has only two elements. Referencing element 3 would raise error ORA-06533.

Example 5-5 Nested Table of Local Type

DECLARE TYPE Roster IS TABLE OF VARCHAR2(15); -- nested table type -- nested table variable initialized with constructor: names Roster := Roster('D Caruso', 'J Hamil', 'D Piro', 'R Singh'); PROCEDURE print_names (heading VARCHAR2) IS BEGIN DBMS_OUTPUT.PUT_LINE(heading); FOR i IN names.FIRST .. names.LAST LOOP -- For first to last element DBMS_OUTPUT.PUT_LINE(names(i)); END LOOP; DBMS_OUTPUT.PUT_LINE('---'); END; BEGIN print_names('Initial Values:'); names(3) := 'P Perez'; -- Change value of one element print_names('Current Values:'); names := Roster('A Jansen', 'B Gupta'); -- Change entire table print_names('Current Values:'); END; /

Result:

Initial Values: D Caruso J Hamil D Piro R Singh --- Current Values: D Caruso J Hamil P Perez R Singh --- Current Values: A Jansen B Gupta

Example 5-6 defines a standalone nested table type, , and a standalone procedure to print a variable of that type, . (The procedure uses the collection methods and , described in "Collection Methods".) An anonymous block declares a variable of type , initializing it to empty with a constructor, and invokes twice: After initializing the variable and after using a constructor to the change the values of all elements.

Example 5-6 Nested Table of Standalone Type

CREATE OR REPLACE TYPE nt_type IS TABLE OF NUMBER; / CREATE OR REPLACE PROCEDURE print_nt (nt nt_type) IS i NUMBER; BEGIN i := nt.FIRST; IF i IS NULL THEN DBMS_OUTPUT.PUT_LINE('nt is empty'); ELSE WHILE i IS NOT NULL LOOP DBMS_OUTPUT.PUT('nt.(' || i || ') = '); print(nt(i)); i := nt.NEXT(i); END LOOP; END IF; DBMS_OUTPUT.PUT_LINE('---'); END print_nt; / DECLARE nt nt_type := nt_type(); -- nested table variable initialized to empty BEGIN print_nt(nt); nt := nt_type(90, 9, 29, 58); print_nt(nt); END; /

Result:

nt is empty --- nt.(1) = 90 nt.(2) = 9 nt.(3) = 29 nt.(4) = 58 ---

Topics

Important Differences Between Nested Tables and Arrays

Conceptually, a nested table is like a one-dimensional array with an arbitrary number of elements. However, a nested table differs from an array in these important ways:

  • An array has a declared number of elements, but a nested table does not. The size of a nested table can increase dynamically.

  • An array is always dense. A nested array is dense initially, but it can become sparse, because you can delete elements from it.

Figure 5-2 shows the important differences between a nested table and an array.

Appropriate Uses for Nested Tables

A nested table is appropriate when:

  • The number of elements is not set.

  • Index values are not consecutive.

  • You must delete or update some elements, but not all elements simultaneously.

    Nested table data is stored in a separate store table, a system-generated database table. When you access a nested table, the database joins the nested table with its store table. This makes nested tables suitable for queries and updates that affect only some elements of the collection.

  • You would create a separate lookup table, with multiple entries for each row of the main table, and access it through join queries.

Collection Constructors

Note:

This topic applies only to varrays and nested tables. Associative arrays do not have constructors. In this topic, collection means varray or nested table.

A collection constructor (constructor) is a system-defined function with the same name as a collection type, which returns a collection of that type. The syntax of a constructor invocation is:

collection_type ( [ value [, value ]... ] )

If the parameter list is empty, the constructor returns an empty collection. Otherwise, the constructor returns a collection that contains the specified values. For semantic details, see "collection_constructor".

You can assign the returned collection to a collection variable (of the same type) in the variable declaration and in the executable part of a block.

Example 5-7 invokes a constructor twice: to initialize the varray variable to empty in its declaration, and to give it new values in the executable part of the block. The procedure shows the initial and final values of . To determine when is empty, uses the collection method , described in "Collection Methods". (For an example of a procedure that prints a varray that might be null, see Example 5-24.)

Example 5-7 Initializing Collection (Varray) Variable to Empty

DECLARE TYPE Foursome IS VARRAY(4) OF VARCHAR2(15); team Foursome := Foursome(); -- initialize to empty PROCEDURE print_team (heading VARCHAR2) IS BEGIN DBMS_OUTPUT.PUT_LINE(heading); IF team.COUNT = 0 THEN DBMS_OUTPUT.PUT_LINE('Empty'); ELSE FOR i IN 1..4 LOOP DBMS_OUTPUT.PUT_LINE(i || '.' || team(i)); END LOOP; END IF; DBMS_OUTPUT.PUT_LINE('---'); END; BEGIN print_team('Team:'); team := Foursome('John', 'Mary', 'Alberto', 'Juanita'); print_team('Team:'); END; /

Result:

Team: Empty --- Team: 1.John 2.Mary 3.Alberto 4.Juanita ---

Assigning Values to Collection Variables

You can assign a value to a collection variable in these ways:

  • Invoke a constructor to create a collection and assign it to the collection variable, as explained in "Collection Constructors".

  • Use the assignment statement (described in "Assignment Statement") to assign it the value of another existing collection variable.

  • Pass it to a subprogram as an or parameter, and then assign the value inside the subprogram.

To assign a value to a scalar element of a collection variable, reference the element as and assign it a value as instructed in "Assigning Values to Variables".

Topics

Data Type Compatibility

You can assign a collection to a collection variable only if they have the same data type. Having the same element type is not enough.

In Example 5-8, types and have the same element type, . Collection variables and have the same data type, , but collection variable has the data type . The assignment of to succeeds, but the assignment of to fails.

Example 5-8 Data Type Compatibility for Collection Assignment

DECLARE TYPE triplet IS VARRAY(3) OF VARCHAR2(15); TYPE trio IS VARRAY(3) OF VARCHAR2(15); group1 triplet := triplet('Jones', 'Wong', 'Marceau'); group2 triplet;group3 trio; BEGIN group2 := group1; -- succeeds group3 := group1; -- fails END; /

Result:

ERROR at line 10: ORA-06550: line 10, column 13: PLS-00382: expression is of wrong type ORA-06550: line 10, column 3: PL/SQL: Statement ignored

Assigning Null Values to Varray or Nested Table Variables

To a varray or nested table variable, you can assign the value or a null collection of the same data type. Either assignment makes the variable null.

Example 5-7 initializes the nested table variable to a non-null value; assigns a null collection to it, making it null; and re-initializes it to a different non-null value.

Example 5-9 Assigning Null Value to Nested Table Variable

DECLARE TYPE dnames_tab IS TABLE OF VARCHAR2(30); dept_names dnames_tab := dnames_tab( 'Shipping','Sales','Finance','Payroll'); -- Initialized to non-null value empty_set dnames_tab; -- Not initialized, therefore null PROCEDURE print_dept_names_status IS BEGIN IF dept_names IS NULL THEN DBMS_OUTPUT.PUT_LINE('dept_names is null.'); ELSE DBMS_OUTPUT.PUT_LINE('dept_names is not null.'); END IF; END print_dept_names_status; BEGIN print_dept_names_status; dept_names := empty_set; -- Assign null collection to dept_names. print_dept_names_status; dept_names := dnames_tab ( 'Shipping','Sales','Finance','Payroll'); -- Re-initialize dept_names print_dept_names_status; END; /

Result:

dept_names is not null. dept_names is null. dept_names is not null.

Assigning Set Operation Results to Nested Table Variables

To a nested table variable, you can assign the result of a SQL operation or SQL function invocation.

The SQL operators combine two nested tables into a single nested table. The elements of the two nested tables must have comparable data types. For information about the operators, see Oracle Database SQL Language Reference.

The SQL function takes a nested table argument and returns a nested table of the same data type whose elements are distinct (the function eliminates duplicate elements). For information about the function, see Oracle Database SQL Language Reference.

Example 5-10 assigns the results of several operations and one function invocation of the nested table variable , using the procedure to print after each assignment. The procedure use the collection methods and , described in "Collection Methods".

Example 5-10 Assigning Set Operation Results to Nested Table Variable

DECLARE TYPE nested_typ IS TABLE OF NUMBER; nt1 nested_typ := nested_typ(1,2,3); nt2 nested_typ := nested_typ(3,2,1); nt3 nested_typ := nested_typ(2,3,1,3); nt4 nested_typ := nested_typ(1,2,4); answer nested_typ; PROCEDURE print_nested_table (nt nested_typ) IS output VARCHAR2(128); BEGIN IF nt IS NULL THEN DBMS_OUTPUT.PUT_LINE('Result: null set'); ELSIF nt.COUNT = 0 THEN DBMS_OUTPUT.PUT_LINE('Result: empty set'); ELSE FOR i IN nt.FIRST .. nt.LAST LOOP -- For first to last element output := output || nt(i) || ' '; END LOOP; DBMS_OUTPUT.PUT_LINE('Result: ' || output); END IF; END print_nested_table; BEGIN answer := nt1 MULTISET UNION nt4; print_nested_table(answer); answer := nt1 MULTISET UNION nt3; print_nested_table(answer); answer := nt1 MULTISET UNION DISTINCT nt3; print_nested_table(answer); answer := nt2 MULTISET INTERSECT nt3; print_nested_table(answer); answer := nt2 MULTISET INTERSECT DISTINCT nt3; print_nested_table(answer); answer := SET(nt3); print_nested_table(answer); answer := nt3 MULTISET EXCEPT nt2; print_nested_table(answer); answer := nt3 MULTISET EXCEPT DISTINCT nt2; print_nested_table(answer); END; /

Result:

Result: 1 2 3 1 2 4 Result: 1 2 3 2 3 1 3 Result: 1 2 3 Result: 3 2 1 Result: 3 2 1 Result: 2 3 1 Result: 3 Result: empty set

Multidimensional Collections

Although a collection has only one dimension, you can model a multidimensional collection with a collection whose elements are collections.

In Example 5-11, is a two-dimensional varray—a varray of varrays of integers.

Example 5-11 Two-Dimensional Varray (Varray of Varrays)

DECLARE TYPE t1 IS VARRAY(10) OF INTEGER; -- varray of integer va t1 := t1(2,3,5); TYPE nt1 IS VARRAY(10) OF t1; -- varray of varray of integer nva nt1 := nt1(va, t1(55,6,73), t1(2,4), va); i INTEGER; va1 t1; BEGIN i := nva(2)(3); DBMS_OUTPUT.PUT_LINE('i = ' || i); nva.EXTEND; nva(5) := t1(56, 32); -- replace inner varray elements nva(4) := t1(45,43,67,43345); -- replace an inner integer element nva(4)(4) := 1; -- replace 43345 with 1 nva(4).EXTEND; -- add element to 4th varray element nva(4)(5) := 89; -- store integer 89 there END; /

Result:

i = 73

In Example 5-12, is a nested table of nested tables of strings, and is a nested table of varrays of integers.

Example 5-12 Nested Tables of Nested Tables and Varrays of Integers

DECLARE TYPE tb1 IS TABLE OF VARCHAR2(20); -- nested table of strings vtb1 tb1 := tb1('one', 'three'); TYPE ntb1 IS TABLE OF tb1; -- nested table of nested tables of strings vntb1 ntb1 := ntb1(vtb1); TYPE tv1 IS VARRAY(10) OF INTEGER; -- varray of integers TYPE ntb2 IS TABLE OF tv1; -- nested table of varrays of integers vntb2 ntb2 := ntb2(tv1(3,5), tv1(5,7,3)); BEGIN vntb1.EXTEND; vntb1(2) := vntb1(1); vntb1.DELETE(1); -- delete first element of vntb1 vntb1(2).DELETE(1); -- delete first string from second table in nested table END; /

In Example 5-13, is an associative array of associative arrays, and is a nested table of varrays of strings.

Example 5-13 Nested Tables of Associative Arrays and Varrays of Strings

DECLARE TYPE tb1 IS TABLE OF INTEGER INDEX BY PLS_INTEGER; -- associative arrays v4 tb1; v5 tb1; TYPE aa1 IS TABLE OF tb1 INDEX BY PLS_INTEGER; -- associative array of v2 aa1; -- associative arrays TYPE va1 IS VARRAY(10) OF VARCHAR2(20); -- varray of strings v1 va1 := va1('hello', 'world'); TYPE ntb2 IS TABLE OF va1 INDEX BY PLS_INTEGER; -- associative array of varrays v3 ntb2; BEGIN v4(1) := 34; -- populate associative array v4(2) := 46456; v4(456) := 343; v2(23) := v4; -- populate associative array of associative arrays v3(34) := va1(33, 456, 656, 343); -- populate associative array varrays v2(35) := v5; -- assign empty associative array to v2(35) v2(35)(2) := 78; END; /

Collection Comparisons

You cannot compare associative array variables to the value or to each other.

Except for Comparing Nested Tables for Equality and Inequality, you cannot natively compare two collection variables with relational operators (listed in Table 2-5). This restriction also applies to implicit comparisons. For example, a collection variable cannot appear in a , , or clause.

To determine if one collection variable is less than another (for example), you must define what less than means in that context and write a function that returns or . For information about writing functions, see Chapter 8, "PL/SQL Subprograms."

Topics

Comparing Varray and Nested Table Variables to NULL

You can compare varray and nested table variables to the value with the "IS [NOT] NULL Operator", but not with the relational operators equal () and not equal (, , , or ).

Example 5-14 compares a varray variable and a nested table variable to correctly.

Example 5-14 Comparing Varray and Nested Table Variables to NULL

DECLARE TYPE Foursome IS VARRAY(4) OF VARCHAR2(15); -- VARRAY type team Foursome; -- varray variable TYPE Roster IS TABLE OF VARCHAR2(15); -- nested table type names Roster := Roster('Adams', 'Patel'); -- nested table variable BEGIN IF team IS NULL THEN DBMS_OUTPUT.PUT_LINE('team IS NULL'); ELSE DBMS_OUTPUT.PUT_LINE('team IS NOT NULL'); END IF; IF names IS NOT NULL THEN DBMS_OUTPUT.PUT_LINE('names IS NOT NULL'); ELSE DBMS_OUTPUT.PUT_LINE('names IS NULL'); END IF; END; /

Result:

team IS NULL names IS NOT NULL

Comparing Nested Tables for Equality and Inequality

If two nested table variables have the same nested table type, and that nested table type does not have elements of a record type, then you can compare the two variables for equality or inequality with the relational operators equal () and not equal (, , , ). Two nested table variables are equal if and only if they have the same set of elements (in any order).

Example 5-15 compares nested table variables for equality and inequality with relational operators.

Example 5-15 Comparing Nested Tables for Equality and Inequality

DECLARE TYPE dnames_tab IS TABLE OF VARCHAR2(30); -- element type is not record type dept_names1 dnames_tab := dnames_tab('Shipping','Sales','Finance','Payroll'); dept_names2 dnames_tab := dnames_tab('Sales','Finance','Shipping','Payroll'); dept_names3 dnames_tab := dnames_tab('Sales','Finance','Payroll'); BEGIN IF dept_names1 = dept_names2 THEN DBMS_OUTPUT.PUT_LINE('dept_names1 = dept_names2'); END IF; IF dept_names2 != dept_names3 THEN DBMS_OUTPUT.PUT_LINE('dept_names2 != dept_names3'); END IF; END; /

Result:

dept_names1 = dept_names2dept_names2 != dept_names3

Comparing Nested Tables with SQL Multiset Conditions

You can compare nested table variables, and test some of their properties, with SQL multiset conditions (described in Oracle Database SQL Language Reference).

Example 5-16 uses the SQL multiset conditions and two SQL functions that take nested table variable arguments, (described in Oracle Database SQL Language Reference) and (described in Oracle Database SQL Language Reference).

Example 5-16 Comparing Nested Tables with SQL Multiset Conditions

DECLARE TYPE nested_typ IS TABLE OF NUMBER; nt1 nested_typ := nested_typ(1,2,3); nt2 nested_typ := nested_typ(3,2,1); nt3 nested_typ := nested_typ(2,3,1,3); nt4 nested_typ := nested_typ(1,2,4); PROCEDURE testify ( truth BOOLEAN := NULL, quantity NUMBER := NULL ) IS BEGIN IF truth IS NOT NULL THEN DBMS_OUTPUT.PUT_LINE ( CASE truth WHEN TRUE THEN 'True' WHEN FALSE THEN 'False' END ); END IF; IF quantity IS NOT NULL THEN DBMS_OUTPUT.PUT_LINE(quantity); END IF; END; BEGIN testify(truth => (nt1 IN (nt2,nt3,nt4))); -- condition testify(truth => (nt1 SUBMULTISET OF nt3)); -- condition testify(truth => (nt1 NOT SUBMULTISET OF nt4)); -- condition testify(truth => (4 MEMBER OF nt1)); -- condition testify(truth => (nt3 IS A SET)); -- condition testify(truth => (nt3 IS NOT A SET)); -- condition testify(truth => (nt1 IS EMPTY)); -- condition testify(quantity => (CARDINALITY(nt3))); -- function testify(quantity => (CARDINALITY(SET(nt3)))); -- 2 functions END; /

Result:

True True True False False True False 4 3

Collection Methods

A collection method is a PL/SQL subprogram—either a function that returns information about a collection or a procedure that operates on a collection. Collection methods make collections easier to use and your applications easier to maintain. Table 5-2 summarizes the collection methods.

Note:

With a null collection, is the only collection method that does not raise the predefined exception .

Table 5-2 Collection Methods

MethodTypeDescription

Procedure

Deletes elements from collection.

Procedure

Deletes elements from end of varray or nested table.

Procedure

Adds elements to end of varray or nested table.

Function

Returns if and only if specified element of varray or nested table exists.

Function

Returns first index in collection.

Function

Returns last index in collection.

Function

Returns number of elements in collection.

Function

Returns maximum number of elements that collection can have.

Function

Returns index that precedes specified index.

Function

Returns index that succeeds specified index.


The basic syntax of a collection method invocation is:

collection_name.method

For detailed syntax, see "Collection Method Invocation".

A collection method invocation can appear anywhere that an invocation of a PL/SQL subprogram of its type (function or procedure) can appear, except in a SQL statement. (For general information about PL/SQL subprograms, see Chapter 8, "PL/SQL Subprograms.")

In a subprogram, a collection parameter assumes the properties of the argument bound to it. You can apply collection methods to such parameters. For varray parameters, the value of is always derived from the parameter type definition, regardless of the parameter mode.

Topics

DELETE Collection Method

is a procedure that deletes elements from a collection. This method has these forms:

  • deletes all elements from a collection of any type.

    This operation immediately frees the memory allocated to the deleted elements.

  • From an associative array or nested table (but not a varray):

    • deletes the element whose index is n, if that element exists; otherwise, it does nothing.

    • deletes all elements whose indexes are in the range m..n, if both m and n exist and m <= n; otherwise, it does nothing.

    For these two forms of , PL/SQL keeps placeholders for the deleted elements. Therefore, the deleted elements are included in the internal size of the collection, and you can restore a deleted element by assigning a valid value to it.

Example 5-17 declares a nested table variable, initializing it with six elements; deletes and then restores the second element; deletes a range of elements and then restores one of them; and then deletes all elements. The restored elements occupy the same memory as the corresponding deleted elements. The procedure prints the nested table variable after initialization and after each operation. The type and procedure are defined in Example 5-6.

Example 5-17 DELETE Method with Nested Table

DECLARE nt nt_type := nt_type(11, 22, 33, 44, 55, 66); BEGIN print_nt(nt); nt.DELETE(2); -- Delete second element print_nt(nt); nt(2) := 2222; -- Restore second element print_nt(nt); nt.DELETE(2, 4); -- Delete range of elements print_nt(nt); nt(3) := 3333; -- Restore third element print_nt(nt); nt.DELETE; -- Delete all elements print_nt(nt); END; /

Result:

nt.(1) = 11 nt.(2) = 22 nt.(3) = 33 nt.(4) = 44 nt.(5) = 55 nt.(6) = 66 --- nt.(1) = 11 nt.(3) = 33 nt.(4) = 44 nt.(5) = 55 nt.(6) = 66 --- nt.(1) = 11 nt.(2) = 2222 nt.(3) = 33 nt.(4) = 44 nt.(5) = 55 nt.(6) = 66 --- nt.(1) = 11 nt.(5) = 55 nt.(6) = 66 --- nt.(1) = 11 nt.(3) = 3333 nt.(5) = 55 nt.(6) = 66 --- nt is empty ---

Example 5-18 populates an associative array indexed by string and deletes all elements, which frees the memory allocated to them. Next, the example replaces the deleted elements—that is, adds new elements that have the same indexes as the deleted elements. The new replacement elements do not occupy the same memory as the corresponding deleted elements. Finally, the example deletes one element and then a range of elements. The procedure shows the effects of the operations.

Example 5-18 DELETE Method with Associative Array Indexed by String

DECLARE TYPE aa_type_str IS TABLE OF INTEGER INDEX BY VARCHAR2(10); aa_str aa_type_str; PROCEDURE print_aa_str IS i VARCHAR2(10); BEGIN i := aa_str.FIRST; IF i IS NULL THEN DBMS_OUTPUT.PUT_LINE('aa_str is empty'); ELSE WHILE i IS NOT NULL LOOP DBMS_OUTPUT.PUT('aa_str.(' || i || ') = '); print(aa_str(i)); i := aa_str.NEXT(i); END LOOP; END IF; DBMS_OUTPUT.PUT_LINE('---'); END print_aa_str; BEGIN aa_str('M') := 13; aa_str('Z') := 26; aa_str('C') := 3; print_aa_str; aa_str.DELETE; -- Delete all elements print_aa_str; aa_str('M') := 13; -- Replace deleted element with same valueaa_str('Z') := 260; -- Replace deleted element with new valueaa_str('C') := 30; -- Replace deleted element with new value aa_str('W') := 23; -- Add new element aa_str('J') := 10; -- Add new element aa_str('N') := 14; -- Add new element aa_str('P') := 16; -- Add new element aa_str('W') := 23; -- Add new element aa_str('J') := 10; -- Add new element print_aa_str; aa_str.DELETE('C'); -- Delete one element print_aa_str; aa_str.DELETE('N','W'); -- Delete range of elements print_aa_str; aa_str.DELETE('Z','M'); -- Does nothing print_aa_str; END; /

Result:

aa_str.(C) = 3 aa_str.(M) = 13 aa_str.(Z) = 26 --- aa_str is empty --- aa_str.(C) = 30 aa_str.(J) = 10 aa_str.(M) = 13 aa_str.(N) = 14 aa_str.(P) = 16 aa_str.(W) = 23 aa_str.(Z) = 260 --- aa_str.(J) = 10 aa_str.(M) = 13 aa_str.(N) = 14 aa_str.(P) = 16 aa_str.(W) = 23 aa_str.(Z) = 260 --- aa_str.(J) = 10 aa_str.(M) = 13 aa_str.(Z) = 260 --- aa_str.(J) = 10 aa_str.(M) = 13 aa_str.(Z) = 260 ---

TRIM Collection Method

is a procedure that deletes elements from the end of a varray or nested table. This method has these forms:

  • removes one element from the end of the collection, if the collection has at least one element; otherwise, it raises the predefined exception .

  • removes n elements from the end of the collection, if there are at least n elements at the end; otherwise, it raises the predefined exception .

operates on the internal size of a collection. That is, if deletes an element but keeps a placeholder for it, then considers the element to exist. Therefore, can delete a deleted element.

PL/SQL does not keep placeholders for trimmed elements. Therefore, trimmed elements are not included in the internal size of the collection, and you cannot restore a trimmed element by assigning a valid value to it.

Caution:

Do not depend on interaction between and . Treat nested tables like either fixed-size arrays (and use only ) or stacks (and use only and ).

Example 5-19 declares a nested table variable, initializing it with six elements; trims the last element; deletes the fourth element; and then trims the last two elements—one of which is the deleted fourth element. The procedure prints the nested table variable after initialization and after the and operations. The type and procedure are defined in Example 5-6.

Example 5-19 TRIM Method with Nested Table

DECLARE nt nt_type := nt_type(11, 22, 33, 44, 55, 66); BEGIN print_nt(nt); nt.TRIM; -- Trim last element print_nt(nt); nt.DELETE(4); -- Delete fourth element print_nt(nt); nt.TRIM(2); -- Trim last two elements print_nt(nt); END; /

Result:

nt.(1) = 11 nt.(2) = 22 nt.(3) = 33 nt.(4) = 44 nt.(5) = 55 nt.(6) = 66 --- nt.(1) = 11 nt.(2) = 22 nt.(3) = 33 nt.(4) = 44 nt.(5) = 55 --- nt.(1) = 11 nt.(2) = 22 nt.(3) = 33 nt.(5) = 55 --- nt.(1) = 11 nt.(2) = 22 nt.(3) = 33 ---

EXTEND Collection Method

is a procedure that adds elements to the end of a varray or nested table. The collection can be empty, but not null. (To make a collection empty or add elements to a null collection, use a constructor. For more information, see "Collection Constructors".)

The method has these forms:

  • appends one null element to the collection.

  • appends n null elements to the collection.

  • , appends n copies of the ith element to the collection.

    Note:

    , is the only form that you can use for a collection whose elements have the constraint.

operates on the internal size of a collection. That is, if deletes an element but keeps a placeholder for it, then considers the element to exist.

Example 5-20 declares a nested table variable, initializing it with three elements; appends two copies of the first element; deletes the fifth (last) element; and then appends one null element. Because considers the deleted fifth element to exist, the appended null element is the sixth element. The procedure prints the nested table variable after initialization and after the and operations. The type and procedure are defined in Example 5-6.

Example 5-20 EXTEND Method with Nested Table

DECLARE nt nt_type := nt_type(11, 22, 33); BEGIN print_nt(nt); nt.EXTEND(2,1); -- Append two copies of first element print_nt(nt); nt.DELETE(5); -- Delete fifth element print_nt(nt); nt.EXTEND; -- Append one null element print_nt(nt); END; /

Result:

nt.(1) = 11 nt.(2) = 22 nt.(3) = 33 --- nt.(1) = 11 nt.(2) = 22 nt.(3) = 33 nt.(4) = 11 nt.(5) = 11 --- nt.(1) = 11 nt.(2) = 22 nt.(3) = 33 nt.(4) = 11 --- nt.(1) = 11 nt.(2) = 22 nt.(3) = 33 nt.(4) = 11 nt.(6) = NULL ---

EXISTS Collection Method

is a function that tells you whether the specified element of a varray or nested table exists.

returns if the nth element of the collection exists and otherwise. If n is out of range, returns instead of raising the predefined exception .

For a deleted element, returns , even if kept a placeholder for it.

Example 5-21 initializes a nested table with four elements, deletes the second element, and prints either the value or status of elements 1 through 6.

Example 5-21 EXISTS Method with Nested Table

DECLARE TYPE NumList IS TABLE OF INTEGER; n NumList := NumList(1,3,5,7); BEGIN n.DELETE(2); -- Delete second element FOR i IN 1..6 LOOP IF n.EXISTS(i) THEN DBMS_OUTPUT.PUT_LINE('n(' || i || ') = ' || n(i)); ELSE DBMS_OUTPUT.PUT_LINE('n(' || i || ') does not exist'); END IF; END LOOP; END; /

Result:

n(1) = 1 n(2) does not exist n(3) = 5 n(4) = 7 n(5) does not exist n(6) does not exist

FIRST and LAST Collection Methods

and are functions. If the collection has at least one element, and return the indexes of the first and last elements, respectively (ignoring deleted elements, even if kept placeholders for them). If the collection has only one element, and return the same index. If the collection is empty, and return .

Topics

FIRST and LAST Methods for Associative Array

For an associative array indexed by , the first and last elements are those with the smallest and largest indexes, respectively.

Example 5-22 shows the values of and for an associative array indexed by , deletes the first and last elements, and shows the values of and again.

Example 5-22 FIRST and LAST Values for Associative Array Indexed by PLS_INTEGER

DECLARE TYPE aa_type_int IS TABLE OF INTEGER INDEX BY PLS_INTEGER; aa_int aa_type_int; PROCEDURE print_first_and_last IS BEGIN DBMS_OUTPUT.PUT_LINE('FIRST = ' || aa_int.FIRST); DBMS_OUTPUT.PUT_LINE('LAST = ' || aa_int.LAST); END print_first_and_last; BEGIN aa_int(1) := 3; aa_int(2) := 6; aa_int(3) := 9; aa_int(4) := 12; DBMS_OUTPUT.PUT_LINE('Before deletions:'); print_first_and_last; aa_int.DELETE(1);aa_int.DELETE(4); DBMS_OUTPUT.PUT_LINE('After deletions:'); print_first_and_last; END; /

Result:

Before deletions: FIRST = 1 LAST = 4 After deletions: FIRST = 2 LAST = 3

For an associative array indexed by string, the first and last elements are those with the lowest and highest key values, respectively. Key values are in sorted order (for more information, see "NLS Parameter Values Affect Associative Arrays Indexed by String").

Example 5-23 shows the values of and for an associative array indexed by string, deletes the first and last elements, and shows the values of and again.

Example 5-23 FIRST and LAST Values for Associative Array Indexed by String

DECLARE TYPE aa_type_str IS TABLE OF INTEGER INDEX BY VARCHAR2(10); aa_str aa_type_str; PROCEDURE print_first_and_last IS BEGIN DBMS_OUTPUT.PUT_LINE('FIRST = ' || aa_str.FIRST); DBMS_OUTPUT.PUT_LINE('LAST = ' || aa_str.LAST); END print_first_and_last; BEGIN aa_str('Z') := 26; aa_str('A') := 1; aa_str('K') := 11; aa_str('R') := 18; DBMS_OUTPUT.PUT_LINE('Before deletions:'); print_first_and_last; aa_str.DELETE('A');aa_str.DELETE('Z'); DBMS_OUTPUT.PUT_LINE('After deletions:'); print_first_and_last; END; /

Result:

Before deletions: FIRST = A LAST = Z After deletions: FIRST = K LAST = R

FIRST and LAST Methods for Varray

For a varray that is not empty, always returns 1. For every varray, always equals (see Example 5-26).

Example 5-24 prints the varray using a statement with the bounds . and .. Because a varray is always dense, inside the loop always exists.

Example 5-24 Printing Varray with FIRST and LAST in FOR LOOP

DECLARE TYPE team_type IS VARRAY(4) OF VARCHAR2(15); team team_type; PROCEDURE print_team (heading VARCHAR2) IS BEGIN DBMS_OUTPUT.PUT_LINE(heading); IF team IS NULL THEN DBMS_OUTPUT.PUT_LINE('Does not exist'); ELSIF team.FIRST IS NULL THEN DBMS_OUTPUT.PUT_LINE('Has no members'); ELSE FOR i IN team.FIRST..team.LAST LOOP DBMS_OUTPUT.PUT_LINE(i || '. ' || team(i)); END LOOP; END IF; DBMS_OUTPUT.PUT_LINE('---'); END; BEGIN print_team('Team Status:'); team := team_type(); -- Team is funded, but nobody is on it. print_team('Team Status:'); team := team_type('John', 'Mary'); -- Put 2 members on team. print_team('Initial Team:'); team := team_type('Arun', 'Amitha', 'Allan', 'Mae'); -- Change team. print_team('New Team:'); END; /

Result:

Team Status: Does not exist --- Team Status: Has no members --- Initial Team: 1. John 2. Mary --- New Team: 1. Arun 2. Amitha 3. Allan 4. Mae ---

FIRST and LAST Methods for Nested Table

For a nested table, equals unless you delete elements from its middle, in which case is larger than (see Example 5-27).

Example 5-25 prints the nested table using a statement with the bounds . and .. Because a nested table can be sparse, the statement prints only if . is .

Example 5-25 Printing Nested Table with FIRST and LAST in FOR LOOP

DECLARE TYPE team_type IS TABLE OF VARCHAR2(15); team team_type; PROCEDURE print_team (heading VARCHAR2) IS BEGIN DBMS_OUTPUT.PUT_LINE(heading); IF team IS NULL THEN DBMS_OUTPUT.PUT_LINE('Does not exist'); ELSIF team.FIRST IS NULL THEN DBMS_OUTPUT.PUT_LINE('Has no members'); ELSE FOR i IN team.FIRST..team.LAST LOOP DBMS_OUTPUT.PUT(i || '. '); IF team.EXISTS(i) THEN DBMS_OUTPUT.PUT_LINE(team(i)); ELSE DBMS_OUTPUT.PUT_LINE('(to be hired)'); END IF; END LOOP; END IF; DBMS_OUTPUT.PUT_LINE('---'); END; BEGIN print_team('Team Status:'); team := team_type(); -- Team is funded, but nobody is on it. print_team('Team Status:'); team := team_type('Arun', 'Amitha', 'Allan', 'Mae'); -- Add members. print_team('Initial Team:'); team.DELETE(2,3); -- Remove 2nd and 3rd members. print_team('Current Team:'); END; /

Result:

Team Status: Does not exist --- Team Status: Has no members --- Initial Team: 1. Arun 2. Amitha 3. Allan 4. Mae --- Current Team: 1. Arun 2. (to be hired) 3. (to be hired) 4. Mae ---

COUNT Collection Method

is a function that returns the number of elements in the collection (ignoring deleted elements, even if kept placeholders for them).

Topics

COUNT Method for Varray

For a varray, always equals . If you increase or decrease the size of a varray (with the or method), the value of changes.

Example 5-26 shows the values of and for a varray after initialization with four elements, after , and after .

Example 5-26 COUNT and LAST Values for Varray

DECLARE TYPE NumList IS VARRAY(10) OF INTEGER; n NumList := NumList(1,3,5,7); PROCEDURE print_count_and_last IS BEGIN DBMS_OUTPUT.PUT('n.COUNT = ' || n.COUNT || ', '); DBMS_OUTPUT.PUT_LINE('n.LAST = ' || n.LAST); END print_count_and_last; BEGIN print_count_and_last; n.EXTEND(3); print_count_and_last; n.TRIM(5); print_count_and_last; END; /

Result:

n.COUNT = 4, n.LAST = 4 n.COUNT = 7, n.LAST = 7 n.COUNT = 2, n.LAST = 2

COUNT Method for Nested Table

For a nested table, equals unless you delete elements from the middle of the nested table, in which case is smaller than .

Example 5-27 shows the values of and for a nested table after initialization with four elements, after deleting the third element, and after adding two null elements to the end. Finally, the example prints the status of elements 1 through 8.

Example 5-27 COUNT and LAST Values for Nested Table

DECLARE TYPE NumList IS TABLE OF INTEGER; n NumList := NumList(1,3,5,7); PROCEDURE print_count_and_last IS BEGIN DBMS_OUTPUT.PUT('n.COUNT = ' || n.COUNT || ', '); DBMS_OUTPUT.PUT_LINE('n.LAST = ' || n.LAST); END print_count_and_last; BEGIN print_count_and_last; n.DELETE(3); -- Delete third element print_count_and_last; n.EXTEND(2); -- Add two null elements to end print_count_and_last; FOR i IN 1..8 LOOP IF n.EXISTS(i) THEN IF n(i) IS NOT NULL THEN DBMS_OUTPUT.PUT_LINE('n(' || i || ') = ' || n(i)); ELSE DBMS_OUTPUT.PUT_LINE('n(' || i || ') = NULL'); END IF; ELSE DBMS_OUTPUT.PUT_LINE('n(' || i || ') does not exist'); END IF; END LOOP; END; /

Result:

n.COUNT = 4, n.LAST = 4 n.COUNT = 3, n.LAST = 4 n.COUNT = 5, n.LAST = 6 n(1) = 1 n(2) = 3 n(3) does not exist n(4) = 7 n(5) = NULL n(6) = NULL n(7) does not exist n(8) does not exist

LIMIT Collection Method

is a function that returns the maximum number of elements that the collection can have. If the collection has no maximum number of elements, returns . Only a varray has a maximum size.

Example 5-28 and prints the values of and for an associative array with four elements, a varray with two elements, and a nested table with three elements.

Example 5-28 LIMIT and COUNT Values for Different Collection Types

DECLARE TYPE aa_type IS TABLE OF INTEGER INDEX BY PLS_INTEGER; aa aa_type; -- associative array TYPE va_type IS VARRAY(4) OF INTEGER; va va_type := va_type(2,4); -- varray TYPE nt_type IS TABLE OF INTEGER; nt nt_type := nt_type(1,3,5); -- nested table BEGIN aa(1):=3; aa(2):=6; aa(3):=9; aa(4):= 12; DBMS_OUTPUT.PUT('aa.COUNT = '); print(aa.COUNT); DBMS_OUTPUT.PUT('aa.LIMIT = '); print(aa.LIMIT); DBMS_OUTPUT.PUT('va.COUNT = '); print(va.COUNT); DBMS_OUTPUT.PUT('va.LIMIT = '); print(va.LIMIT); DBMS_OUTPUT.PUT('nt.COUNT = '); print(nt.COUNT); DBMS_OUTPUT.PUT('nt.LIMIT = '); print(nt.LIMIT); END; /

Result:

aa.COUNT = 4 aa.LIMIT = NULL va.COUNT = 2 va.LIMIT = 4 nt.COUNT = 3 nt.LIMIT = NULL

PRIOR and NEXT Collection Methods

and are functions that let you move backward and forward in the collection (ignoring deleted elements, even if kept placeholders for them). These methods are useful for traversing sparse collections.

Given an index:

  • returns the index of the preceding existing element of the collection, if one exists. Otherwise, returns .

    For any collection , returns .

  • returns the index of the succeeding existing element of the collection, if one exists. Otherwise, returns .

    For any collection , returns .

The given index need not exist. However, if the collection is a varray, and the index exceeds , then:

  • returns .

  • returns .

For example:

DECLARE TYPE Arr_Type IS VARRAY(10) OF NUMBER; v_Numbers Arr_Type := Arr_Type(); BEGIN v_Numbers.EXTEND(4); v_Numbers (1) := 10; v_Numbers (2) := 20; v_Numbers (3) := 30; v_Numbers (4) := 40; DBMS_OUTPUT.PUT_LINE(NVL(v_Numbers.prior (3400), -1)); DBMS_OUTPUT.PUT_LINE(NVL(v_Numbers.next (3400), -1)); END; /

Result:

4 -1

Example 5-29 initializes a nested table with six elements, deletes the fourth element, and then shows the values of and for elements 1 through 7. Elements 4 and 7 do not exist. Element 2 exists, despite its null value.

Example 5-29 PRIOR and NEXT Methods

DECLARE TYPE nt_type IS TABLE OF NUMBER; nt nt_type := nt_type(18, NULL, 36, 45, 54, 63); BEGIN nt.DELETE(4); DBMS_OUTPUT.PUT_LINE('nt(4) was deleted.'); FOR i IN 1..7 LOOP DBMS_OUTPUT.PUT('nt.PRIOR(' || i || ') = '); print(nt.PRIOR(i)); DBMS_OUTPUT.PUT('nt.NEXT(' || i || ') = '); print(nt.NEXT(i)); END LOOP; END; /

Result:

nt(4) was deleted. nt.PRIOR(1) = NULL nt.NEXT(1) = 2 nt.PRIOR(2) = 1 nt.NEXT(2) = 3 nt.PRIOR(3) = 2 nt.NEXT(3) = 5 nt.PRIOR(4) = 3 nt.NEXT(4) = 5 nt.PRIOR(5) = 3 nt.NEXT(5) = 6 nt.PRIOR(6) = 5 nt.NEXT(6) = NULL nt.PRIOR(7) = 6 nt.NEXT(7) = NULL

For an associative array indexed by string, the prior and next indexes are determined by key values, which are in sorted order (for more information, see "NLS Parameter Values Affect Associative Arrays Indexed by String"

TECHNOLOGY: PL/SQL

  

Working with Strings

By Steven Feuerstein

 

Part 3 in a series of articles on understanding and using PL/SQL

Every application needs data. That seems rather obvious, doesn’t it? An application is almost always built on top of database tables. Those tables are full of different kinds of data. And the programs you write—whether they are in PL/SQL or another language—manipulate that data. It is, therefore, extremely important for you to be aware of the different datatypes supported by PL/SQL and how you can work with those datatypes.

Take the Challenge!


Each of my PL/SQL 101 articles offers a quiz to test your knowledge of the information provided in the article. The quiz questions are shown below and also at PL/SQL Challenge (plsqlchallenge.com), a Website that offers online quizzes for the PL/SQL language. You can read and answer the quiz here, and then check your answers in the next issue. If, however, you take the quiz at PL/SQL Challenge, you will be entered into a raffle to win your choice of an e-book from O’Reilly Media (oreilly.com).

Question 1

What will be displayed after executing this block?

 

BEGIN sys.DBMS_OUTPUT.put_line ( INSTR ('steven feuerstein' , 'e' , -1 , 2)); END;

Question 2

True or false: When assigning a literal value to a string, that value may not contain within it any single quotes.
 

Question 3

What will be displayed after executing this block?
 

BEGIN DBMS_OUTPUT.put_line ( 'REPLACE=' || REPLACE ('steven feuerstein' , 'e' , NULL)); DBMS_OUTPUT.put_line ( 'TRANSLATE=' || TRANSLATE ('steven feuerstein' , 'e' , NULL)); END;

As you might expect, there is an awful lot to learn about datatypes, and not all of that knowledge can fit into a single article. So I will start with one of the most common types of data: strings. Very few database tables and programs do not contain strings—strings such as a company name, address information, descriptive text, and so on. As a result, you quite often need to do the following: 

  • Declare string variables and constants

  • Manipulate the contents of a string (remove characters, join together multiple strings, and so on)

  • Move string data between PL/SQL programs and database tables


This article gives you the information you need to begin working with strings in your PL/SQL programs.


What Is a String?

A string, also referred to as character data, is a sequence of selected symbols from a particular set of characters. In other words, the symbols in a string might consist of English letters, such as ”A” or ”B.” They might also consist of Chinese characters, such as 字串.

There are three kinds of strings in PL/SQL:

Fixed-length strings. The string is right-padded with spaces to the length specified in the declaration. (See ”Declaring String Variables,” to see padding in action.)

Variable-length strings. A maximum length for the string is specified (and it must be no greater than 32,767), but no padding takes place.

Character large objects (CLOBs). CLOBs are variable-length strings that can be up to 128 terabytes.

Strings can be literals or variables. A string literal begins and ends with a single quotation mark: 

'This is a string literal'  

If you need to embed a single quote inside a string literal, you can type in two single quotes right next to one another, as in: 

'This isn''t a date'  

You can also use the “q” character to indicate an alternative terminating character for the literal:

q'[This isn't a date]'  

A string variable is an identifier declared with a string datatype and then assigned a value (which could be a literal or an expression).

Declaring String Variables

To work with strings in your PL/SQL programs, you declare variables to hold the string values. To declare a string variable, you must select from one of the many string datatypes Oracle Database offers, including CHAR, NCHAR, VARCHAR2, NVARCHAR2, CLOB, and NCLOB. The datatypes that are prefixed with an ”N” are “national character set” datatypes, which means they are used to store Unicode character data. (Unicode is a universal encoded character set that can store information in any language using a single character set.)

To declare a variable-length string, you must provide the maximum length of that string. The following code declares a variable, using the VARCHAR2 datatype, that will hold a company name, which cannot (in this declaration) have more than 100 characters: 

DECLARE l_company_name VARCHAR2(100);  

You must provide the maximum length; if you leave it out, Oracle Database raises a compile error, as shown below: 

SQL> DECLARE 2 l_company_name VARCHAR2; 3 BEGIN 4 l_company_name := 'Oracle Corporation'; 5 END; 6 / l_company_name VARCHAR2; * ERROR at line 2: ORA-06550: line 2, column 21: PLS-00215: String length constraints must be in range (1 .. 32767)  

To declare a fixed-length string, use the CHAR datatype: 

DECLARE l_yes_or_no CHAR(1) := 'Y';  

With CHAR (unlike with VARCHAR2) you do not have to specify a maximum length for a fixed-length variable. If you leave off the length constraint, Oracle Database automatically uses a maximum length of 1. In other words, the two declarations below are identical: 

DECLARE l_yes_or_no1 CHAR(1) := 'Y'; l_yes_or_no2 CHAR := 'Y';  

If you declare a CHAR variable with a length greater than 1, Oracle Database automatically pads whatever value you assign to that variable with spaces to the maximum length specified.

Finally, to declare a character large object, use the CLOB datatype. You do not specify a maximum length; the length is determined automatically by Oracle Database and is based on the database block size. Here is an example: 

DECLARE l_lots_of_text CLOB;  

So, how do you determine which datatype to use in your programs? Here are some guidelines: 

  • If your string might contain more than 32,767 characters, use the CLOB (or NCLOB) datatype.

  • If the value assigned to a string always has a fixed length (such as a U.S. Social Security number, which always has the same format and length, NNN-NN-NNNN), use CHAR (or NCHAR).

  • Otherwise (and, therefore, most of the time), use the VARCHAR2 datatype (or NVACHAR2, when working with Unicode data).

Using the CHAR datatype for anything but strings that always have a fixed number of characters can lead to unexpected and undesirable results. Consider the following block, which mixes variable and fixed-length strings:
 

DECLARE l_variable VARCHAR2 (10) := 'Logic'; l_fixed CHAR (10) := 'Logic'; BEGIN IF l_variable = l_fixed THEN DBMS_OUTPUT.put_line ('Equal'); ELSE DBMS_OUTPUT.put_line ('Not Equal'); END IF; END;  

At first glance, you would expect that the word “Equal” would be displayed after execution. That is not the case. Instead, “Not Equal” is displayed, because the value of l_fixed has been padded to a length of 10 with spaces. Consider the padding demonstrated in the following block; you would expect the block to display “Not Equal”:

BEGIN IF 'Logic' = 'Logic ' THEN DBMS_OUTPUT.put_line ('Equal'); ELSE DBMS_OUTPUT.put_line ('Not Equal'); END IF; END;  

You should, as a result, be very careful about the use of the CHAR datatype, whether as the type of a variable, database column, or parameter.

Once you have declared a variable, you can assign it a value, change its value, and perform operations on the string contained in that variable using string functions and operators.

For the rest of this article, I focus on the VARCHAR2 datatype.

Using Built-in Functions with Strings

Once you assign a string to a variable, you most likely need to analyze the contents of that string, change its value in some way, or combine it with other strings. Oracle Database offers a wide array of built-in functions to help you with all such requirements. Let’s take a look at the most commonly used of these functions.

Concatenate multiple strings. One of the most basic and frequently needed operations on strings is to combine or concatenate them together. PL/SQL offers two ways to do this: 

  • The CONCAT built-in function

  • The || (concatenation) operator

 The CONCAT function accepts two strings as its arguments and returns those two strings “stuck together.” The concatenation operator also concatenates together two strings, but it is easier to use when combining more than two strings, as you can see in this example: 

DECLARE l_first VARCHAR2 (10) := 'Steven'; l_middle VARCHAR2 (5) := 'Eric'; l_last VARCHAR2 (20) := 'Feuerstein'; BEGIN /* Use the CONCAT function */ DBMS_OUTPUT.put_line ( CONCAT ('Steven', 'Feuerstein')); /* Use the || operator */ DBMS_OUTPUT.put_line ( l_first || ' ' || l_middle || ' ' || l_last); END; / 

The output from this block is: 

StevenFeuerstein Steven Eric Feuerstein

 
In my experience, you rarely encounter the CONCAT function. Instead, the || operator is almost universally used by PL/SQL developers.

If either of the strings passed to CONCAT or || is NULL or ‘’ (a zero-length string), both the function and the operator simply return the non-NULL string. If both strings are NULL, NULL is returned.

Change the case of a string. Three built-in functions change the case of characters in a string: 

  • UPPER changes all characters to uppercase.

  • LOWER changes all characters to lowercase.

  • INITCAP changes the first character of each word to uppercase (characters are delimited by a white space or non-alphanumeric character).

 Listing 1 shows some examples that use these case-changing functions.

Code Listing 1: Examples of case-changing functions 

SQL> DECLARE 2 l_company_name VARCHAR2 (25) := 'oraCLE corporatION'; 3 BEGIN 4 DBMS_OUTPUT.put_line (UPPER (l_company_name)); 5 DBMS_OUTPUT.put_line (LOWER (l_company_name)); 6 DBMS_OUTPUT.put_line (INITCAP (l_company_name)); 7 END; 8 / ORACLE CORPORATION oracle corporation Oracle Corporation  

Extract part of a string. One of the most commonly utilized built-in functions for strings is SUBSTR, which is used to extract a substring from a string. When calling SUBSTR, you provide the string, the position at which the desired substring starts, and the number of characters in the substring.

Listing 2 shows some examples that use the SUBSTR function.

Code Listing 2: Examples of SUBSTR function 

DECLARE l_company_name VARCHAR2 (6) := 'Oracle'; BEGIN /* Retrieve the first character in the string */ DBMS_OUTPUT.put_line ( SUBSTR (l_company_name, 1, 1)); /* Retrieve the last character in the string */ DBMS_OUTPUT.put_line ( SUBSTR (l_company_name, -1, 1)); /* Retrieve three characters, starting from the second position. */ DBMS_OUTPUT.put_line ( SUBSTR (l_company_name, 2, 3)); /* Retrieve the remainder of the string, starting from the second position. */ DBMS_OUTPUT.put_line ( SUBSTR (l_company_name, 2)); END; /  

The output from this block is: 

O e rac racle  

As you can see, with the SUBSTR function you can specify a negative starting position for the substring, in which case Oracle Database counts backward from the end of the string. If you do not provide a third argument—the number of characters in the substring—Oracle Database automatically returns the remainder of the string from the specified position.

Find a string within another string. Use the INSTR function to determine where (and if) a string appears within another string. INSTR accepts as many as four arguments: 

  • The string to be searched (required).

  • The substring of interest (required).

  • The starting position of the search (optional). If the value is negative, count from the end of the string. If no value is provided, Oracle Database starts at the beginning of the string; that is, the starting position is 1.

  • The Nth occurrence of the substring (optional). If no value is provided, Oracle Database looks for the first occurrence.

 Listing 3 shows some examples that use the INSTR function.

Code Listing 3: Examples of INSTR function 

BEGIN /* Find the location of the first "e" */ DBMS_OUTPUT.put_line ( INSTR ('steven feuerstein', 'e')); /* Find the location of the first "e" starting from position 6 */ DBMS_OUTPUT.put_line ( INSTR ('steven feuerstein' , 'e' , 6)); /* Find the location of the first "e" starting from the 6th position from the end of string and counting to the left. */ DBMS_OUTPUT.put_line ( INSTR ('steven feuerstein' , 'e' , -6)); /* Find the location of the 3rd "e" starting from the 6th position from the end of string. */ DBMS_OUTPUT.put_line ( INSTR ('steven feuerstein' , 'e' , -6 , 3)); END; /  

The output from this block is: 

3 9 11 5  

INSTR is a very flexible and handy utility. It can easily be used to determine whether or not a substring appears at all in a string. Here is a Boolean function that does just that: 

CREATE OR REPLACE FUNCTION is_in_string ( string_in IN VARCHAR2 ,substring_in IN VARCHAR2) RETURN BOOLEAN IS BEGIN RETURN INSTR (string_in , substring_in) > 0; END is_in_string; /  

Pad a string with spaces (or other characters). I warned earlier about using the CHAR datatype, because Oracle Database pads your string value with spaces to the maximum length specified in the declaration.

However, there are times, primarily when generating reports, when you want to put spaces (or other characters) in front of or after the end of your string. For these situations, Oracle Database offers LPAD and RPAD.

When you call these functions, you specify the length to which you want your string padded and with what character or characters. If you do not specify any pad characters, Oracle Database defaults to padding with spaces.

Listing 4 shows some examples that use these LPAD and RPAD padding functions.

Code Listing 4: Examples of padding functions 

DECLARE l_first VARCHAR2 (10) := 'Steven'; l_last VARCHAR2 (20) := 'Feuerstein'; l_phone VARCHAR2 (20) := '773-426-9093'; BEGIN /* Indent the subheader by 3 characters */ DBMS_OUTPUT.put_line ('Header'); DBMS_OUTPUT.put_line ( LPAD ('Sub-header', 13, '.')); /* Add "123" to the end of the string, until the 20 character is reached.*/ DBMS_OUTPUT.put_line ( RPAD ('abc', 20, '123')); /* Display headers and then values to fit within the columns. */ DBMS_OUTPUT.put_line ( /*1234567890x12345678901234567890x*/ 'First Name Last Name Phone'); DBMS_OUTPUT.put_line ( RPAD (l_first, 10) || ' ' || RPAD (l_last, 20) || ' ' || l_phone); END; /  

The output from this block is: 

Header ...Sub-header abc12312312312312312 First Name Last Name Phone Steven Feuerstein 773-426-9093  

Replace characters in a string. Oracle Database provides a number of functions that allow you to selectively change one or more characters in a string. You might need, for example, to replace all spaces in a string with the HTML equivalent (“ ”) so the text is displayed properly in a browser. Two functions take care of such needs for you: 

  • REPLACE replaces a set or pattern of characters with another set.

  • TRANSLATE translates or replaces individual characters.

Listing 5 shows some examples of these two character-replacement built-in functions. Notice that when you are replacing a single character, the effect of REPLACE and TRANSLATE is the same. When replacing multiple characters, REPLACE and TRANSLATE act differently. The call to REPLACE asked that appearances of “abc” be replaced with “123.” If, however, any of the individual characters (a, b, or c) appeared in the string outside of this pattern (“abc”), they would not be replaced.

Code Listing 5: Examples of character replacement functions 

DECLARE l_name VARCHAR2 (50) := 'Steven Feuerstein'; BEGIN /* Replace all e's with the number 2. Since you are replacing a single character, you can use either REPLACE or TRANSLATE. */ DBMS_OUTPUT.put_line ( REPLACE (l_name, 'e', '2')); DBMS_OUTPUT.put_line ( TRANSLATE (l_name, 'e', '2')); /* Replace all instances of "abc" with "123" */ DBMS_OUTPUT.put_line ( REPLACE ('abc-a-b-c-abc' , 'abc' , '123')); /* Replace "a" with "1", "b" with "2", "c" with "3". */ DBMS_OUTPUT.put_line ( TRANSLATE ('abc-a-b-c-abc' , 'abc' , '123')); END; /  

The output from this block is: 

St2v2n F2u2rst2in St2v2n F2u2rst2in 123-a-b-c-123 123-1-2-3-123  

The call to TRANSLATE, however, specified that any occurrence of each of the individual characters be replaced with the character in the third argument in the same position.

Generally, you should use REPLACE whenever you need to replace a pattern of characters, while TRANSLATE is best applied to situations in which you need to replace or substitute individual characters in the string.

Remove characters from a string. What LPAD and RPAD giveth, TRIM, LTRIM, and RTRIM taketh away. Use these trim functions to remove characters from either the beginning (left) or end (right) of the string. Listing 6 shows an example of both RTRIM and LTRIM.

Code Listing 6: Examples of LTRIM and RTRIM functions 

DECLARE a VARCHAR2 (40) := 'This sentence has too many periods....'; b VARCHAR2 (40) := 'The number 1'; BEGIN DBMS_OUTPUT.put_line ( RTRIM (a, '.')); DBMS_OUTPUT.put_line ( LTRIM ( b , 'ABCDEFGHIJKLMNOPQRSTUVWXYZ ' || 'abcdefghijklmnopqrstuvwxyz')); END;  

The output from this block is: 

This sentence has too many periods 1  

RTRIM removed all the periods, because the second argument specifies the character (or characters) to trim, in this case, a period. The call to LTRIM demonstrates that you can specify multiple characters to trim. In this case, I asked that all letters and spaces be trimmed from the beginning of string b, and I got what I asked for.

The default behavior of both RTRIM and LTRIM is to trim spaces from the beginning or end of the string. Specifying RTRIM(a) is the same as asking for RTRIM(a,’ ‘). The same goes for LTRIM(a) and LTRIM(a,’ ‘).

The other trimming function is just plain TRIM. TRIM works a bit differently from LTRIM and RTRIM, as you can see in this block: 

DECLARE x VARCHAR2 (30) := '.....Hi there!.....'; BEGIN DBMS_OUTPUT.put_line ( TRIM (LEADING '.' FROM x)); DBMS_OUTPUT.put_line ( TRIM (TRAILING '.' FROM x)); DBMS_OUTPUT.put_line ( TRIM (BOTH '.' FROM x)); --The default is to trim --from both sides DBMS_OUTPUT.put_line ( TRIM ('.' FROM x)); --The default trim character --is the space: DBMS_OUTPUT.put_line (TRIM (x)); END;

 
The output from this block is: 

Hi there!..... .....Hi there! Hi there! Hi there! .....Hi there!.....

 
With TRIM, you can trim from either side or from both sides. However, you can specify only a single character to remove. You cannot, for example, write the following: 

TRIM(BOTH ',.;' FROM x)

 
If you need to remove more than one character from the front and back of a string, you need to use RTRIM and LTRIM: 

RTRIM(LTRIM(x,',.;'),',.;')

 
You can also use TRANSLATE to remove characters from a string by replacing them with (or “translating” them into) NULL. You must, however, take care with how you specify this replacement. Suppose I want to remove all digits (0 through 9) from a string. My first attempt yields the following block: 

BEGIN /* Remove all digits (0-9) from the string. */ DBMS_OUTPUT.put_line ( TRANSLATE ('S1t2e3v4e56n' , '1234567890' , '')); END; /

 
When I execute this block, however, nothing (well, a NULL string) is displayed. This happens because if any of the arguments passed to TRANSLATE are NULL (or a zero-length string), the function returns a NULL value.

So all three arguments must be non-NULL, which means that you need to put at the start of the second and third arguments a character that will simply be replaced with itself, as in the following: 

BEGIN /* Remove all digits (0-9) from the string. */ DBMS_OUTPUT.put_line ( TRANSLATE ('S1t2e3v4e56n' , 'A1234567890' , 'A')); END; /

 
Now, “A” is replaced with “A” and the remaining characters in the string are replaced with NULL, so the string “Steven” is then displayed.

Good to Know

Beyond awareness of the basic properties of strings in PL/SQL and built-in functions, you can benefit by keeping the following points about long strings and maximum string sizes in mind.

When the string is too long. You must specify a maximum length when you declare a variable based on the VARCHAR2 type. What happens, then, when you try to assign a value to that variable whose length is greater than the maximum? Oracle Database raises the ORA-06502 error, which is also defined in PL/SQL as the VALUE_ERROR exception.

Here is an example of the exception being raised and propagated out of the block unhandled: 

SQL> DECLARE 2 l_name VARCHAR2(3); 3 BEGIN 4 l_name := 'Steven'; 5 END; 6 / DECLARE * ERROR at line 1: ORA-06502: PL/SQL: numeric or value error: character string buffer too small ORA-06512: at line 4

 
Here is a rewrite of the same block that traps the VALUE_ERROR exception: 

SQL> DECLARE 2 l_name VARCHAR2 (3); 3 BEGIN 4 l_name := 'Steven'; 5 EXCEPTION 6 WHEN VALUE_ERROR 7 THEN 8 DBMS_OUTPUT.put_line ( 9 'Value too large!'); 10 END; 11 / Value too large!   Interestingly, if you try to insert or update a value in a VARCHAR2 column of a database table, Oracle Database raises a different error, which you can see below:  SQL> CREATE TABLE small_varchar2 2 ( 3 string_value VARCHAR2 (2) 4 ) 5 / Table created. SQL> BEGIN 2 INSERT INTO small_varchar2 3 VALUES ('abc'); 4 END; 5 / BEGIN * ERROR at line 1: ORA-12899: value too large for column "HR"."SMALL_VARCHAR2"."STRING_VALUE" (actual: 3, maximum: 2) ORA-06512: at line 2  

Different maximum sizes. There are a number of differences between SQL and PL/SQL for the maximum sizes for string datatypes. In PL/SQL, the maximum size for VARCHAR2 is 32,767 bytes, while in SQL the maximum is 4,000 bytes. In PL/SQL, the maximum size for CHAR is 32,767 bytes, while in SQL the maximum is 2,000 bytes.

Therefore, if you need to save a value from a VARCHAR2 variable in the column of a table, you might encounter the ORA-12899 error. If this happens, you have two choices: 

  • Use SUBSTR to extract no more than 4,000 bytes from the larger string, and save that substring to the table. This option clearly has a drawback: you lose some of your data.

  • Change the datatype of the column from VARCHAR2 to CLOB. This way, you can save all your data.

In PL/SQL, the maximum size for CLOB is 128 terabytes, while in SQL the maximum is just (4 GB - 1) * DB_BLOCK_SIZE.


There’s More to Data than Strings

Character data plays a very large role in PL/SQL applications, but those same applications undoubtedly also rely on data of other types, especially numbers and dates. I will cover these datatypes in the next PL/SQL 101 article. 



Steven Feuerstein
's biography and links to more of his Oracle Magazine PL/SQL articles

 

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