SELECT a.attname as column_name
                                     , i.relname as index_name
                                 FROM  pg_class t
                                     , pg_class i
                                     , pg_index ix
                                     , pg_attribute a
                                WHERE t.oid = ix.indrelid
                                  AND i.oid = ix.indexrelid
                                  AND a.attrelid = t.oid
                                  AND a.attnum = ANY(ix.indkey)
                                  AND i.relname = 'customers_composite_idx'
                                  AND t.relname = 'customers'