Subquery not in performance question
I have this slow query
select * from table1 where id NOT IN ( select id from table2 )
Would this be faster by doing something like (not sure if this is possible):
select * from table1 where id not in ( select id from table2 where id = table1.id )
Or:
select * from table1 where table1.id NOT EXIST( select id from table2 where table2.id = table1.id )
Or:
select * from table1
left join table2 on table2.id = table1.id
WHERE table2.id is 开发者_运维百科null
Or do something else? Like break it up into two queries ...
The question is - are the field(s) in the comparison nullable (meaning, can the column value be NULL)?
If they're nullable...
...in MySQL the NOT IN
or NOT EXISTS
perform better - see this link.
If they are NOT nullable...
... LEFT JOIN / IS NULL
performs better - see this link.
select table1.* from table1
LEFT JOIN table2 ON table1.id = table2.id
WHERE table2.id IS NULL
The object being to get rid of NOT IN
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