-----Original Message----- From: Igor Neyman Sent: Thursday, September 22, 2016 10:33 AM To: 'Sven R. Kunze' <srku...@mail.de>; pgsql-performance@postgresql.org Subject: RE: [PERFORM] Multiple-Table-Spanning Joins with ORs in WHERE Clause
-----Original Message----- From: pgsql-performance-ow...@postgresql.org [mailto:pgsql-performance-ow...@postgresql.org] On Behalf Of Sven R. Kunze Sent: Thursday, September 22, 2016 9:25 AM To: pgsql-performance@postgresql.org Subject: [PERFORM] Multiple-Table-Spanning Joins with ORs in WHERE Clause Hi pgsql-performance list, what is the recommended way of doing **multiple-table-spanning joins with ORs in the WHERE-clause**? Until now, we've used the LEFT OUTER JOIN to filter big_table like so: SELECT DISTINCT <fields of big_table> FROM "big_table" LEFT OUTER JOIN "table_a" ON ("big_table"."id" = "table_a"."big_table_id") LEFT OUTER JOIN "table_b" ON ("big_table"."id" = "table_b"."big_table_id") WHERE "table_a"."item_id" IN (<handful of items>) OR "table_b"."item_id" IN (<handful of items>); However, this results in an awful slow plan (requiring to scan the complete big_table which obviously isn't optimal). So, we decided (at least for now) to split up the query into two separate ones and merge/de-duplicate the result with application logic: SELECT <fields of big_table> FROM "big_table" INNER JOIN "table_a" ON ("big_table"."id" = "table_a"."big_table_id") WHERE "table_a"."item_id" IN (<handful of items>); SELECT <fields of big_table> FROM "big_table" INNER JOIN "table_b" ON ("big_table"."id" = "table_b"."big_table_id") WHERE "table_b"."item_id" IN (<handful of items>); As you can imagine we would be very glad to solve this issue with a single query and without having to re-code existing logic of PostgreSQL. But how? Best, Sven PS: if you require EXPLAIN ANALYZE, I can post them as well. ______________________________________________________________________________________________ Another option to try:: SELECT DISTINCT <fields of big_table> FROM "big_table" LEFT OUTER JOIN "table_a" ON ("big_table"."id" = "table_a"."big_table_id" AND "table_a"."item_id" IN (<handful of items>)) LEFT OUTER JOIN "table_b" ON ("big_table"."id" = "table_b"."big_table_id" AND "table_b"."item_id" IN (<handful of items>)); Regards, Igor Neyman -- Sent via pgsql-performance mailing list (pgsql-performance@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-performance
