Question

现有两个表A和B，它们具有一个相同字段，请问如何查找A表中有而B表中没有的记录？

Answer 1

select * form A left join B on (A.相同字段 != '' and B.相同字段 = '');

Answer 2

Select id From A Where Id Not in(Select Id From B)

Answer 3

select a.*
from a as a left join b as b on a.id=b.id
where b.id is null

Answer 4

select * from A where id not in(select id from B)