Subscript Generating Functions

Updated on 2024-09-30 GMT+08:00

View PDF

generate_subscripts(array anyarray, dim int)

Description: Generates a series comprising the given array's subscripts.

Return type: setof int

Example:

    
       SELECT generate_subscripts('{NULL,1,NULL,2}'::int[], 1) AS s;
 s 
---
 1
 2
 3
 4
(4 rows)

generate_subscripts(array anyarray, dim int, reverse boolean)

Description: Generates a series comprising the given array's subscripts. When reverse is true, the series is returned in reverse order.

Return type: setof int

Example:

    
       SELECT generate_subscripts('{NULL,1,NULL,2}'::int[], 1,TRUE) AS s;
 s
---
 4
 3
 2
 1
(4 rows)

generate_subscripts is a function that generates the set of valid subscripts for the specified dimension of a given array. Zero rows are returned for arrays that do not have the requested dimension, or for NULL arrays (but valid subscripts are returned for NULL array elements). Example:

   
    
      
      -- unnest a 2D array
CREATE OR REPLACE FUNCTION unnest2(anyarray)
RETURNS SETOF anyelement AS $$
SELECT $1[i][j]
   FROM generate_subscripts($1,1) g1(i),
        generate_subscripts($1,2) g2(j);
$$ LANGUAGE sql IMMUTABLE;

SELECT * FROM unnest2(ARRAY[[1,2],[3,4]]);
 unnest2 
---------
       1
       2
       3
       4
(4 rows)

     

   
  