Collections in Oracle

Index-By Tables (Associative Arrays)

The first type of collection is known as index-by tables. These behave in the same way as arrays except that have no upper bounds, allowing them to constantly extend. As the name implies, the collection is indexed using BINARY_INTEGER values, which do not need to be consecutive. The collection is extended by assigning values to an element using an index value that does not currently exist.

SET SERVEROUTPUT ON SIZE 1000000
DECLARE
  TYPE table_type IS TABLE OF NUMBER(10)
    INDEX BY BINARY_INTEGER;
  
  v_tab  table_type;
  v_idx  NUMBER;
BEGIN
  -- Initialise the collection.
  << load_loop >>
  FOR i IN 1 .. 5 LOOP
    v_tab(i) := i;
  END LOOP load_loop;
  
  -- Delete the third item of the collection.
  v_tab.DELETE(3);
  
  -- Traverse sparse collection
  v_idx := v_tab.FIRST;
  << display_loop >>
  WHILE v_idx IS NOT NULL LOOP
    DBMS_OUTPUT.PUT_LINE('The number ' || v_tab(v_idx));
    v_idx := v_tab.NEXT(v_idx);
  END LOOP display_loop;
END;
/

The number 1
The number 2
The number 4
The number 5

PL/SQL procedure successfully completed.

SQL>

In Oracle 9i Release 2 these have been renamed to Associative Arrays and can be indexed by BINARY INTEGER or VARCHAR2.

 

Nested Table Collections

Nested table collections are an extension of the index-by tables. The main difference between the two is that nested tables can be stored in a database column but index-by tables cannot. In addition some DML operations are possible on nested tables when they are stored in the database. During creation the collection must be dense, having consecutive subscripts for the elements. Once created elements can be deleted using the DELETE method to make the collection sparse. The NEXT method overcomes the problems of traversing sparse collections.

SET SERVEROUTPUT ON SIZE 1000000
DECLARE
  TYPE table_type IS TABLE OF NUMBER(10);
  v_tab  table_type;
  v_idx  NUMBER;
BEGIN

  -- Initialise the collection with two values.
  v_tab := table_type(1, 2);

  -- Extend the collection with extra values.
  << load_loop >>
  FOR i IN 3 .. 5 LOOP
    v_tab.extend;
    v_tab(v_tab.last) := i;
  END LOOP load_loop;
  
  -- Delete the third item of the collection.
  v_tab.DELETE(3);
  
  -- Traverse sparse collection
  v_idx := v_tab.FIRST;
  << display_loop >>
  WHILE v_idx IS NOT NULL LOOP
    DBMS_OUTPUT.PUT_LINE('The number ' || v_tab(v_idx));
    v_idx := v_tab.NEXT(v_idx);
  END LOOP display_loop;
END;
/

The number 1
The number 2
The number 4
The number 5

PL/SQL procedure successfully completed.

SQL>

 

Varray Collections

VARRAY is similar to a nested table except you must specifiy an upper bound in the declaration. Like nested tables they can be stored in the database, but unlike nested tables individual elements cannot be deleted so they remain dense.

SET SERVEROUTPUT ON SIZE 1000000
DECLARE
  TYPE table_type IS VARRAY(5) OF NUMBER(10);
  v_tab  table_type;
  v_idx  NUMBER;
BEGIN
  -- Initialise the collection with two values.
  v_tab := table_type(1, 2);

  -- Extend the collection with extra values.
  << load_loop >>
  FOR i IN 3 .. 5 LOOP
    v_tab.extend;
    v_tab(v_tab.last) := i;
  END LOOP load_loop;
  
  -- Can't delete from a VARRAY.
  -- v_tab.DELETE(3);

  -- Traverse collection
  v_idx := v_tab.FIRST;
  << display_loop >>
  WHILE v_idx IS NOT NULL LOOP
    DBMS_OUTPUT.PUT_LINE('The number ' || v_tab(v_idx));
    v_idx := v_tab.NEXT(v_idx);
  END LOOP display_loop;
END;
/

The number 1
The number 2
The number 3
The number 4
The number 5

PL/SQL procedure successfully completed.

SQL>

Extending the load_loop to 3..6 attempts to extend the VARRAY beyond it’s limit of 5 elements resulting in the following error.

DECLARE
*
ERROR at line 1:
ORA-06532: Subscript outside of limit
ORA-06512: at line 12

 

https://oracle-base.com/articles/8i/collections-8i

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