subselects - which is faster?
От | Cedar Cox |
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Тема | subselects - which is faster? |
Дата | |
Msg-id | Pine.LNX.4.21.0306121259480.3203-100000@nanu.visionforisrael.com обсуждение исходный текст |
Ответы |
Re: subselects - which is faster?
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Список | pgsql-sql |
It's been a while since I've done much SQL.. . I'm wondering which of these two queries is faster (both get the same result)? . Which one is more correct? Does it even matter or are they the same? The first one reads easier to me. . What's the difference between "InitPlan" and "SubPlan"? explain SELECT eqid, (select name from tbleqattrtypes where id= (select eqattrtypeid from tbleqattrs where id=main.eqattrid))asattrtype, eqattrid from tbleqattrmap as main; NOTICE: QUERY PLAN: Seq Scan on tbleqattrmap main (cost=0.00..1.15 rows=15 width=8) SubPlan -> Seq Scan on tbleqattrtypes (cost=0.00..1.04rows=1 width=12) InitPlan -> Seq Scan on tbleqattrs (cost=0.00..1.09 rows=1 width=4) explain SELECT eqid, (select (select name from tbleqattrtypes where id=sec.eqattrtypeid) from tbleqattrs as secwhere id=main.eqattrid)as attrtype, eqattrid from tbleqattrmap as main; NOTICE: QUERY PLAN: Seq Scan on tbleqattrmap main (cost=0.00..1.15 rows=15 width=8) SubPlan -> Seq Scan on tbleqattrs sec (cost=0.00..1.09rows=1 width=4) SubPlan -> Seq Scan on tbleqattrtypes (cost=0.00..1.04 rows=1 width=12) One additional detail: right now the tables are all very small, and tbleqattrtypes will not grow much, but tbleqattrs will eventually be very large. Thanks, and sorry for bothering you all.. - Cedar
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