PolarDB:Varrays

A varray or variable-size array is a type of collection that associates a positive integer with a value. In many respects, it is similar to a nested table.

A varray has the following characteristics:

• A varray type must be defined along with a maximum size limit. After the varray type is defined, varray variables can be declared of that varray type. Data manipulation occurs by using the varray variable or simply "varray" for short. The number of elements in the varray cannot exceed the maximum size limit established in the varray type definition.
• When a varray variable is declared, the varray initially does not exist (it is a null collection). The null varray must be initialized with a constructor. You can also initialize the varray by using an assignment statement where the right-hand side of the assignment is an initialized varray of the same type.
• The key is a positive integer.
• The constructor establishes the number of elements in the varray, which must not exceed the maximum size limit. The EXTEND method can add additional elements to the varray up to the maximum size limit.
• Unlike a nested table, a varray cannot be sparse - the assignment of values to keys has no gaps.
• An attempt to reference a varray element beyond its initialized or extended size but within the maximum size limit will result in a SUBSCRIPT_BEYOND_COUNT exception.
• An attempt to reference a varray element beyond the maximum size limit or extend a varray beyond the maximum size limit will result in a SUBSCRIPT_OUTSIDE_LIMIT exception.

The TYPE IS VARRAY statement is used to define a varray type within the declaration section of an SPL program:

TYPE varraytype IS { VARRAY | VARYING ARRAY }(maxsize)
  OF { datatype | objtype };

varraytype is an identifier assigned to the varray type. datatype is a scalar data type such as VARCHAR2 or NUMBER. maxsize is the maximum number of elements permitted in varrays of that type. objtype is a previously defined object type.

The CREATE TYPE statement can be used to define a varray type that is available to all SPL programs in the database. To use the varray, a variable must be declared of that varray type. The following is the syntax for declaring a varray variable:

varray varraytype

varray is an identifier assigned to the varray. varraytype is the identifier of a previously defined varray type.

A varray is initialized by using the constructor of the varray type.

varraytype ([ { expr1 | NULL } [, { expr2 | NULL } ]
  [, ...] ])

varraytype is the identifier of the constructor of the varray type, which has the same name as the varray type. expr1, expr2, ... are expressions that are type-compatible with the element type of the varray. If NULL is specified, the corresponding element is set to null. If the parameter list is empty, an empty varray is returned, which means no elements in the varray. If the varray is defined from an object type, exprn must return an object of that object type. The object can be the return value of a function or the return value of the constructor of the object type. The object can also be an element of another varray of the same varray type.

If a collection method other than EXISTS is applied to an uninitialized varray, a COLLECTION_IS_NULL exception is thrown.

The following example shows a constructor for a varray:

DECLARE
    TYPE varray_typ IS VARRAY(2) OF CHAR(1);
    v_varray        varray_typ := varray_typ('A','B');

An element of the varray is referenced by using the following syntax:

varray(n)[.element ]

varray is the identifier of a previously declared varray. n is a positive integer. If the varray type of varray is defined from an object type, [.element ] must reference an attribute within the object type from which the varray type is defined. Alternatively, the entire object can be referenced by omitting [.element ].

The following example shows a varray where it is known that four elements exist:

DECLARE
    TYPE dname_varray_typ IS VARRAY(4) OF VARCHAR2(14);
    dname_varray    dname_varray_typ;
    CURSOR dept_cur IS SELECT dname FROM dept ORDER BY dname;
    i               INTEGER := 0;
BEGIN
    dname_varray := dname_varray_typ(NULL, NULL, NULL, NULL);
    FOR r_dept IN dept_cur LOOP
        i := i + 1;
        dname_varray(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_varray(j));
    END LOOP;
END;

The above example produces the following output:

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