Question

如何编写一个显示成员1和2的电影数量的SQL？

MID =会员ID FID =电影ID 下表说明：议员1名单上有2,3,5,17,21部电影。议员2在他的名单上有5,14,18部电影。

 1. MID ------ | FID
 2. M000001 | F000002
 3. M000001 | F000003
 4. M000001 | F000005
 5. M000001 | F000021
 6. M000002 | F000005
 7. M000002 | F000014
 8. M000002 | F000018
 9. M000003 | F000001
 10. M000003 | F000004
 11. M000003 |F000024

*对不起的桌子感到抱歉。

Answer 1

如果您想要所有对的数字，只需进行自我加入：

select t1.mid, t2.mid, count(*)
from table as t1 inner join
     table as t2
     on t1.fid = t2.fid and t1.mid < t2.mid
group by t1.mid, t2.mid;

如果您想将此限制为仅限两个成员，您可以执行以下操作：

select count(*)
from table as t1 inner join
     table as t2
     on t1.fid = t2.fid and
        t1.mid = 1 and
        t2.mid = 2;

Answer 2

子查询是一种方式。

SELECT COUNT(*) FROM t1 t
WHERE EXISTS (SELECT 1 FROM t1 WHERE Mid = 2 AND Fid = t.Fid)
AND Mid = 1

计算类似的记录

2 个答案: