How to create an index for elements of an array in PostgreSQL?

Question

With this schema:

create table object (
   obj_id      serial      primary key,
   name        varchar(80) not null unique,
   description text,
   tag_arr            


        

Answer 1

This is my workaround, because I see no PostgreSQL optimized internal function for do the same,

CREATE FUNCTION unnest_with_idx(anyarray) RETURNS 
table(idx integer, val anyelement) AS $$ 
   SELECT generate_series(1,array_upper($1,1)) as idx, unnest($1) as val;
$$ LANGUAGE SQL IMMUTABLE;
-- Test:
SELECT idx,val from unnest_with_idx(array[1,20,3,5]) as t;

For check if exists an internal function, see "How to acess array internal index with postgreSQL?" question.

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Edited after @JimNasby comment

Solution for pg9.4+

SELECT * FROM unnest(array[20,11,3,5]) WITH ORDINALITY;

the WITH ORDINALITY produces a new column "ordinality" that is the array-index. See also this tutorial.

In pg9.5+, it works fine also for JSON arrays!

 SELECT * FROM jsonb_array_elements( '[20,11,3,5]'::JSONB ) WITH ORDINALITY