Nested tables v15

A nested table is a type of collection that associates a positive integer with a value. A nested table has the following characteristics:

• You must define a nested table type. After that, you can declare nested table variables of that nested table type. Data manipulation occurs using the nested table variable, also known simply as a table.
• When you declare a nested table variable, the nested table doesn't yet exist. It is a null collection. You must initialize the null table with a constructor. You can also initialize the table by using an assignment statement where the right-hand side of the assignment is an initialized table of the same type. Note: Initialization of a nested table is mandatory in Oracle but optional in SPL.
• The key is a positive integer.
• The constructor establishes the number of elements in the table. The EXTEND method adds elements to the table. For details, see Collection methods. Note: Using the constructor to establish the number of elements in the table and using the EXTEND method to add elements to the table are mandatory in Oracle but optional in SPL.
• The table can be sparse. There can be gaps in assigning values to keys.
• An attempt to reference a table element beyond its initialized or extended size results in a SUBSCRIPT_BEYOND_COUNT exception.

Use the TYPE IS TABLE statement to define a nested table type in the declaration section of an SPL program:

TYPE <tbltype> IS TABLE OF { <datatype> | <rectype> | <objtype> };

Where:

tbltype is an identifier assigned to the nested table type.

datatype is a scalar data type such as VARCHAR2 or NUMBER.

rectype is a previously defined record type.

objtype is a previously defined object type.

To use the table, you must declare a variable of that nested table type. The following is the syntax for declaring a table variable:

<table> <tbltype>

Where:

table is an identifier assigned to the nested table.

tbltype is the identifier of a previously defined nested table type.

Initialize a nested table using the nested table type’s constructor:

<tbltype> ([ { <expr1> | NULL } [, { <expr2> | NULL } ] [, ...] ])

Where:

tbltype is the identifier of the nested table type’s constructor, which has the same name as the nested table type.

expr1, expr2, … are expressions that are type-compatible with the element type of the table. If you specify NULL, the corresponding element is set to null. If the parameter list is empty, then an empty nested table is returned, which means the table has no elements. If the table is defined from an object type, then exprn must return an object of that object type. The object can be the return value of a function or the object type’s constructor. Or the object can be an element of another nested table of the same type.

If you apply a collection method other than EXISTS to an uninitialized nested table, a COLLECTION_IS_NULL exception is thrown. For details, see Collection methods.

This example shows a constructor for a nested table:

DECLARE
    TYPE nested_typ IS TABLE OF CHAR(1);
    v_nested        nested_typ := nested_typ('A','B');

Reference an element of the table using the following syntax:

<table>(<n>)[<.element> ]

Where:

table is the identifier of a previously declared table.

n is a positive integer.

If the table type of table is defined from a record type or object type, then [.element ] must reference an individual field in the record type or attribute in the object type from which the nested table type is defined. Alternatively, you can reference the entire record or object by omitting [.element ].

This example shows a nested table where it's known that there are four elements:

DECLARE
    TYPE dname_tbl_typ IS TABLE OF VARCHAR2(14);
    dname_tbl       dname_tbl_typ;
    CURSOR dept_cur IS SELECT dname FROM dept ORDER BY dname;
    i               INTEGER := 0;
BEGIN
    dname_tbl := dname_tbl_typ(NULL, NULL, NULL, NULL);
    FOR r_dept IN dept_cur LOOP
        i := i + 1;
        dname_tbl(i) := r_dept.dname;
    END LOOP;
    DBMS_OUTPUT.PUT_LINE('DNAME');
    DBMS_OUTPUT.PUT_LINE('----------');
    FOR j IN 1..i LOOP
        DBMS_OUTPUT.PUT_LINE(dname_tbl(j));
    END LOOP;
END;

The following is the output from the example:

DNAME
----------
ACCOUNTING
OPERATIONS
RESEARCH
SALES

This example reads the first 10 employee names from the emp table, stores them in a nested table, and then displays the results from the table. The SPL code is written to assume that the number of employees to return isn't known beforehand.

DECLARE
    TYPE emp_rec_typ IS RECORD (
        empno       NUMBER(4),
        ename       VARCHAR2(10)
    );
    TYPE emp_tbl_typ IS TABLE OF emp_rec_typ;
    emp_tbl         emp_tbl_typ;
    CURSOR emp_cur IS SELECT empno, ename FROM emp WHERE ROWNUM <= 10;
    i               INTEGER := 0;
BEGIN
    emp_tbl := emp_tbl_typ();
    DBMS_OUTPUT.PUT_LINE('EMPNO    ENAME');
    DBMS_OUTPUT.PUT_LINE('-----    -------');
    FOR r_emp IN emp_cur LOOP
        i := i + 1;
        emp_tbl.EXTEND;
        emp_tbl(i) := r_emp;
    END LOOP;
    FOR j IN 1..10 LOOP
        DBMS_OUTPUT.PUT_LINE(emp_tbl(j).empno || '     ' ||
            emp_tbl(j).ename);
    END LOOP;
END;

An empty table with the constructor emp_tbl_typ() is created as the first statement in the executable section of the anonymous block. The EXTEND collection method is then used to add an element to the table for each employee returned from the result set. See Extend.

The following is the output:

EMPNO    ENAME
-----    -------
7369     SMITH
7499     ALLEN
7521     WARD
7566     JONES
7654     MARTIN
7698     BLAKE
7782     CLARK
7788     SCOTT
7839     KING
7844     TURNER

This example shows how you can use a nested table of an object type. First, create an object type with attributes for the department name and location:

CREATE TYPE dept_obj_typ AS OBJECT (
    dname           VARCHAR2(14),
    loc             VARCHAR2(13)
);

This anonymous block defines a nested table type whose element consists of the dept_obj_typ object type. A nested table variable is declared, initialized, and then populated from the dept table. Finally, the elements from the nested table are displayed.

DECLARE
    TYPE dept_tbl_typ IS TABLE OF dept_obj_typ;
    dept_tbl        dept_tbl_typ;
    CURSOR dept_cur IS SELECT dname, loc FROM dept ORDER BY dname;
    i               INTEGER := 0;
BEGIN
    dept_tbl := dept_tbl_typ(
        dept_obj_typ(NULL,NULL),
        dept_obj_typ(NULL,NULL),
        dept_obj_typ(NULL,NULL),
        dept_obj_typ(NULL,NULL)
    );
    FOR r_dept IN dept_cur LOOP
        i := i + 1;
        dept_tbl(i).dname := r_dept.dname;
        dept_tbl(i).loc   := r_dept.loc;
    END LOOP;
    DBMS_OUTPUT.PUT_LINE('DNAME          LOC');
    DBMS_OUTPUT.PUT_LINE('----------     ----------');
    FOR j IN 1..i LOOP
        DBMS_OUTPUT.PUT_LINE(RPAD(dept_tbl(j).dname,14) || ' ' ||
            dept_tbl(j).loc);
    END LOOP;
END;

The parameters that make up the nested table’s constructor, dept_tbl_typ, are calls to the object type’s constructor dept_obj_typ. The following is the output from the anonymous block:

DNAME          LOC
----------     ----------
ACCOUNTING     NEW YORK
OPERATIONS     BOSTON
RESEARCH       DALLAS
SALES          CHICAGO