Re: Optimising a two column OR check

On Sat, 12 Oct 2019 at 17:16, Andrew Gierth <andrew(at)tao11(dot)riddles(dot)org(dot)uk>
wrote:

> >>>>> "Ivan" == Ivan Voras <ivoras(at)gmail(dot)com> writes:
>

> Ivan> SELECT user1_id,user2_id FROM friend WHERE user1_id=42 OR
> user2_id=42;
>
> To get friends of user 42:
>
> SELECT user1_id FROM friend WHERE user2_id=42
> UNION ALL
> SELECT user2_id FROM friend WHERE user1_id=42;
>
> assuming you create the (user2_id,user1_id) index, this should get you
> an Append of two index-only scans. We can use UNION ALL here rather than
> UNION because the table constraints ensure there are no duplicates.
>

Thanks! That's a more elegant solution for my query than what I had in mind!