如何操作两个表使它最有效率，在线等

[zerolx]

有两个表a，b，
a
IdCard*
name

b
ID //编号
IDCard

a表的数据开始已经录入
b表中有部分已经录入

如何在a表中选出b 表中没有的数据？

[xhwly]

select * from a where idcard in
(
select idcard from a where idcard not in (select idcard from b)
)

[welyngj]

SELECT a.* FROM a WHERE NOT EXISTS (SELECT * FROM b WHERE a.IDCard=b.IDCard)

[smalldeer]

exists更有效率

[zhiyuan6600]

select * from a where idcard not in (select id from b)
或者
select *from a where not exist(select id from id=a.idcard)

[loveweb]

select * from a where idcard not in (select distinct idcard from b)

[xiaoyuehen]

下次我也不用not in了...

[太空11]

SELECT a.* FROM a WHERE NOT EXISTS (SELECT * FROM b WHERE a.IDCard=b.IDCard)

[xzx760815]

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

用聯接最快

[uffeng]

楼上的正确

[st_2000]

楼上正解