Accessing index of associative array in SELECT-FROM TABLE() operation

As of Oracle Database 12c Release 1, you can now use the TABLE operator with associative arrays whose types are declared in a package specification. Prior to 12.1, this was only possible with schema-level nested table and varray types. Here's a quick example:

CREATE OR REPLACE PACKAGE aa_pkg AUTHID DEFINER
IS
   TYPE record_t IS RECORD (nm VARCHAR2 (100), sal NUMBER);

   TYPE array_t IS TABLE OF record_t INDEX BY PLS_INTEGER;

   FUNCTION my_array RETURN array_t;
END;
/

 CREATE OR REPLACE PACKAGE BODY aa_pkg
IS
   FUNCTION my_array RETURN array_t
   IS
      l_return   array_t;
   BEGIN
      l_return (1).nm := 'Me'; l_return (1).sal := 1000;
      l_return (200).nm := 'You'; l_return (200).sal := 2;
      RETURN l_return;
   END;
END;
/

 DECLARE
   l_array   aa_pkg.array_t;
BEGIN
   l_array := aa_pkg.my_array;

   FOR rec IN (  SELECT * FROM TABLE (l_array) ORDER BY nm)
   LOOP
      DBMS_OUTPUT.put_line (rec.nm);
   END LOOP;
END;
/

And with nested tables and varrays, the index values used in those collections are usually not very interesting. Varrays are always densely-filled (no gaps between first and last index values). Nested tables are (or should be treated as) multisets - the order of its elements is not significant.

But with associative arrays, index values can be negative. They can be strings. And it is not terribly uncommon for associative arrays to be sparse (not every index value defined between first and last).

What if you need to access those index values in the dataset returned by the TABLE operator? In this case, I am sorry to have to tell you, you have to do some extra work. That information simply isn't available natively - which, I think, is quite reasonable. When you use SELECT-FROM TABLE you are saying, in effect, I want to treat the data as a virtual tables. Tables don't have indexes built into them. You have to specify them "on top" of the table.

In any case, the solution isn't terribly difficult. You simply add a field to your record (or attribute to object type). Or if your collection is currently a collection of scalars (list of dates or strings or numbers), then you will have to create a record or object type to hold that scalar value, plus the index value. Then that index value is available as "just another column" in your query.

Here are the steps:

1. Recompile the package specification, after adding an index field. The package body remains the same as above, so I won't repeat it below.

CREATE OR REPLACE PACKAGE aa_pkg AUTHID DEFINER 
IS 
   TYPE record_t IS RECORD 
   ( 
      idx   INTEGER, 
      nm    VARCHAR2 (100), 
      sal   NUMBER 
   ); 
 
   TYPE array_t IS TABLE OF record_t INDEX BY PLS_INTEGER; 
 
   FUNCTION my_array  RETURN array_t; 
END; 

2. Reference that index value as a column in your query:

DECLARE 
   l_array   aa_pkg.array_t; 
   l_index   PLS_INTEGER; 
BEGIN 
   l_array := aa_pkg.my_array; 
 
   l_index := l_array.FIRST; 
 
   WHILE l_index IS NOT NULL 
   LOOP 
      l_array (l_index).idx := l_index; 
      l_index := l_array.next (l_index); 
   END LOOP; 
 
   FOR rec IN (  SELECT * FROM TABLE (l_array) ORDER BY idx) 
   LOOP 
      DBMS_OUTPUT.put_line (rec.idx || ' = ' || rec.nm); 
   END LOOP; 
END; 


This script can be executed in its entirety on LiveSQL.

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