Uz.ytkownik Stephan Szabo napisa?:
Yes, I meant group_id, but in orginal query I didn't have to add group_id to select list.But you can't do that anyway, because you don't expose group_id in the original query. I assume user_id was a mistake then and was meant to be group_id or that both were meant to be in the select list.
The problem isn't ambigous columns, but speed.In the first case changing the order means that the output group_id column is X.group_id rather than users.group_id (using removes one of them which is why group_id isn't ambiguous. In the second it uses on to get both group_ids and exposes the one from X.
I think Postgres first performs sub-query with all records from table (it takes very long time). After this Postgres permforms joining table with sub-query. The question is: How to speed up query like this? How to give param group_id from first table (users) to subquery?
Tomasz Myrta
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