postgis_constraint_srid(geomschema text, geomtable text, geomcolumn text)

SELECT replace(replace(split_part(s.consrc, ' = ', 2), ')', ''), '(', '')::integer

         FROM pg_class c, pg_namespace n, pg_attribute a

         , (SELECT connamespace, conrelid, conkey, pg_get_constraintdef(oid) As consrc

            FROM pg_constraint) AS s

         WHERE n.nspname = $1

         AND c.relname = $2

         AND a.attname = $3

         AND a.attrelid = c.oid

         AND s.connamespace = n.oid

         AND s.conrelid = c.oid

         AND a.attnum = ANY (s.conkey)

         AND s.consrc LIKE '%srid(% = %';