Postgres split as it can be used for IN clause - sql

Question

I use Postgres 8.1. In my sub function I am returning a string which some ID s are concatenated together. And I need to split those ID s and use them in the WHERE clause from main select query.
for example sub function:
subFunction( 'item_id' character varying )RETURNS character varying AS
-- implementation of sub function---
return concatenatedString;
this concatenatedString like this: 23|32|25|234.
And in my main query
SELECT * FROM tableName WHERE id IN (--need to get ids returning from sub function splitting the string--) .
Is there any way that I can split the string returned by sub function and put the result into the IN clause.
Another approach to solve this : Split PostgreSQL Query filtering

Answer 1

As #JustBob says in his comments, your best bet would be to upgrade to a more recent postgresql version, after which you could use regexp_split_to_table, or regexp_split_to_array and then use array operators instead, eg.
SELECT * FROM tablename WHERE id = ANY (regexp_split_to_array(subFunction(...), '\|'));
However, luckily for you, your string resembles an alternation regex, so you might just be able to get away with this:
SELECT * FROM tablename WHERE id::text ~ '^(' || subFunction(...) || ')$';
This will do a regular expression match against a regex looking like this
^(23|32|25|234)$
which will return true if your id value is in the list.
That should work even in 8.1.