Since you very nicely DID NOT provide the pg version, O/S or table structure(s), which is what you should do REGARDLESS of the
type of question (it's just the smart and polite thing to do when asking for help) The best I can suggest is:SELECT
CASE WHEN context = 'friend' THEN p.junka
WHEN context = 'group' THEN p.junkb
WHEN context = 'both' THEN p.junka || ' ' || p.junkb
END
FROM posting p
where p.author_id in (SELECT f.friend_id
FROM friends f
WHERE f.user_id = ?)
OR p.group_id in (SELECT m.group_id
FROM memberships m
WHERE m.user_id = ?);
On Tue, Apr 28, 2015 at 6:26 PM, Jonathan Vanasco <postgres@xxxxxxxx> wrote:
I'm trying to upgrade some code that powers a newfeed type stream, and hoping someone can offer some insight on better ways to structure some parts of the query
The part that has me stumped right now...
There are several criteria for why something could appear in a stream. for example, here are 2 handling a posting:
* a posting by a friend
* a posting in a group
the general way I've handled this so far has been simple:
select * from posting where author_id in (select friend_id from friends where user_id = ?) or group_id in (select group_id from memberships where user_id = ?);
now i need to pull in the context of the match (friend, group, both), but I can't figure out how to do this cleanly.
1. if i just add 'case' statements to the select to note the origin, those subselects run again. (ie, the same subquery is executed twice)
2. if i structure this as a union (and note the origin with a string), it takes a lot more work to integrate and sort the 2 separate selects ( eg "select id, timestamp, 'by-friend'" unioned with "in-group")
does anyone have ideas on other approaches to structuring this?
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Melvin Davidson
I reserve the right to fantasize. Whether or not you
wish to share my fantasy is entirely up to you.![]()
I reserve the right to fantasize. Whether or not you
wish to share my fantasy is entirely up to you.
