Question

oracle语句，我想查询A表中的a字段下的值不等于B表中b的值的数据，

Answer 1

这个的话，需要用到not in来实现。
select * from A where a not in ( select b from B)；
备注：以上语句就是从B表中先读取出来所有的b的值，之后通过not in函数进行判断，不符合条件的输出结果。

Answer 2

select A.*
from A,B
WHERE A.ID= B.ID
AND A.a<>B.b;

Answer 3

①select * from A where a not in (
select b from B)
② select a from A
minus
select b from B

Answer 4

select * from A where a not in (
select b from B)