Question

select a from TABLE_A where b in （select b from TABLE_B） 请问上面的查询语句，能再优化吗?

Answer 1

select table_a.a
from table_a inner join tableb where table_a.b=table_b.b
连接查询的效率最高，in子句效率很低。。

Answer 2

select a from TABLE_A
inner join TABLE_B on TABLE_A.b=TABLE_B.b
或者
select a from TABLE_A
where exists (select * from TABLE_B where b=TABLE_A.b)

Answer 3

尽量避免in
建议用exist