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Working with Collections in Oracle

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@2017-02-03 15:02:56

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 shwon in the following example. (The function does for the associative array what a constructor does for a varray or nested table.)

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 IS
    Ret My_AA;
  BEGIN
    Ret(-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.
@2017-02-03 15:15:27

Assigning Null Values to Varray or Nested Table Variables

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

The following example initializes the nested table variable dname_tab to a non-null value; assigns a null collection to it, making it null; and re-initializes it to a different non-null value.

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.
@2017-02-03 15:20:39

Assigning Set Operation Results to Nested Table Variables

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

The SQL MULTISET operators combine two nested tables into a single nested table. The elements of the two nested tables must have comparable data types.

The SQL SET 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).

The following example assigns the results of several MULTISET operations and one SET function invocation of the nested table variable answer, using the procedure print_nested_table to print answer after each assignment.

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
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