Re: left outer join with count
| От | Gábor SZŰCS |
|---|---|
| Тема | Re: left outer join with count |
| Дата | |
| Msg-id | CAHEufv3tO3f6gyuP_4Gze8QGh3V-O5AVaJa9+RDckB2LK4d76g@mail.gmail.com обсуждение исходный текст |
| Ответ на | left outer join with count (Gary Stainburn <gary.stainburn@ringways.co.uk>) |
| Ответы |
Re: left outer join with count
|
| Список | pgsql-sql |
Hello Gary,
select sj.*, sr.*,
Depends on way too many things, but assuming
- You are concerned about cardinality of wd Vs SJ
- SJ.sj_id is unique
- there are necessary indexes in place
...
Then I'd recommend subselect in SELECT clause, like:
(select count(sj_id) from work_documents wd where wd.sj_id=SJ.sj_id) doc_count from
service_jobs sj
left outer join service_receptions sr on sr.sr_id = sj.sj_sr_id;
left outer join service_receptions sr on sr.sr_id = sj.sj_sr_id;
(Note, haven't verified syntax)
Maybe if you could send explain plans and index info...
Gary Stainburn <gary.stainburn@ringways.co.uk> ezt írta (időpont: 2020. máj. 29., P 18:09):
I have the following select:
select sj.*, sr.*, wd.doc_count from
service_jobs sj
left outer join service_receptions sr on sr.sr_id = sj.sj_sr_id
left outer join (select sj_id, count(sj_id) as doc_count from work_documents wd group by sj_id) wd on wd.wd_sj_id = sj.sj_id;
While the select works, I can't help thinking that the last join is expensive. Is there a cleaner (quicker) method of doing this?
Gary
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