浅谈sql中的in与not in,exists与not exists的区别

select * from A where cc in(select cc from B)　　-->效率低，用到了A表上cc列的索引；

select * from A where exists(select cc from B where cc=A.cc)　　-->效率高，用到了B表上cc列的索引。

select * from B where cc in(select cc from A)　　-->效率高，用到了B表上cc列的索引

select * from B where exists(select cc from A where cc=B.cc)　　-->效率低，用到了A表上cc列的索引。

create table #t1(c1 int,c2 int);

create table #t2(c1 int,c2 int);

insert into #t1 values(1,2);

insert into #t1 values(1,3);

insert into #t2 values(1,2);

insert into #t2 values(1,null);

 

select * from #t1 where c2 not in(select c2 from #t2);　　-->执行结果：无

select * from #t1 where not exists(select 1 from #t2 where #t2.c2=#t1.c2)　　-->执行结果：1　　3

select name from student where name in('zhang','wang','zhao');

select name from student where name='zhang' or name='wang' or name='zhao'