SQLテクノロジーの内幕-10 inとexistsのパフォーマンス比較
911 ワード
in exists
in hash , exists loop , loop 。
exists in 。
, in exists 。
, , exists, in:
: A( ), B( )
1:
select * from A where cc in (select cc from B)
, A cc ;
select * from A where exists(select cc from B where cc=A.cc)
, B cc 。
2:
select * from B where cc in (select cc from A)
, B cc ;
select * from B where exists(select cc from A where cc=B.cc)
, A cc 。
not in not exists
not in , ;
not extsts 。
, not exists not in 。
in =
select name from student where name in ('zhang','wang','li','zhao');
select name from student where name='zhang' or name='li' or name='wang' or name='zhao'
。