All we need is an easy explanation of the problem, so here it is.
I want to run a query like this:
SELECT *
FROM "core_user"
WHERE UPPER("core_user"."email"::text) = UPPER('[email protected]')
ORDER BY "core_user"."last_login" DESC
LIMIT 1;
I’ve tried adding two indexes:
CREATE INDEX core_user_upper_idx ON public.core_user USING btree (upper((email)::text));
CREATE INDEX core_user_last_lo_0521b8_idx ON public.core_user USING btree (last_login);
core_user_upper_idx works well if I remove the ordering clause, but in its current state explain gives
Limit (cost=0.29..10.33 rows=1 width=431)
-> Index Scan Backward using core_user_last_lo_0521b8_idx on core_user (cost=0.29..5531.53 rows=551 width=431)
Filter: (upper((email)::text) = '[email protected]'::text)
which doesn’t perform very well.
Is there a better index for me to add here? I’m a bit unsure as to whether I should "prioritise" the email or last_login fields.
How to solve :
I know you bored from this bug, So we are here to help you! Take a deep breath and look at the explanation of your problem. We have many solutions to this problem, But we recommend you to use the first method because it is tested & true method that will 100% work for you.
Method 1
A multicolumn expression index should serve your particular query best:
CREATE INDEX ON public.core_user (upper(email), last_login DESC);
If last_login can be NULL, consider NULLS LAST – in index and query.
The rule of thumb is: equality first, range later. See:
Note: Use and implement method 1 because this method fully tested our system.
Thank you 🙂
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