SQL计数WHERE子句

Question

我有喜欢的表：membership_id | user_id | group_id

我正在寻找一个SQL查询来获取公共组的2个不同的用户之间的数。我可以在几个查询中做到这一点，并使用一些PHP，但我想知道是否有一种方法只使用SQL。

像与用户ID 1和3，有3个共同组（1,5和6），所以返回的结果将是3

我做了一些测试，但至今没有结果.. 。谢谢。

Answer 1

你不需要“多WHERE子句”，甚至自连接：

SELECT group_id 
FROM theTable AS t 
WHERE t.user_id IN (1, 3) 
GROUP BY group_id 
HAVING COUNT(DISTINCT user_id) = 2; 

更一般

SELECT group_id 
FROM theTable AS t 
WHERE t.user_id IN ([user id list]) 
GROUP BY group_id 
HAVING COUNT(DISTINCT user_id) = [# of user ids in list]; 

---

编辑：哦，你想要的组数....

SELECT COUNT(1) FROM (
    SELECT group_id 
    FROM theTable AS t 
    WHERE t.user_id IN (1, 3) 
    GROUP BY group_id 
    HAVING COUNT(DISTINCT user_id) = 2 
); 

Answer 2

您可以通过连接来实现此目的。如果你不想串接输出

select t1.user_id, t2.user_id, group_concat(distinct t1.group_id) 
from your_table t1 
join your_table t2 
on t1.user_id < t2.user_id 
and t1.group_id = t2.group_id 
group by t1.user_id, t2.user_id; 

：

select distinct t1.user_id, t2.user_id, t1.group_id 
from your_table t1 
join your_table t2 
on t1.user_id < t2.user_id 
and t1.group_id = t2.group_id; 

Answer 3

尝试加入同一个表的两个实例（为他们每个人只选择记录

试试这个相对于使用GROUP_ID作为连接属性，并计算结果中的一个用户）：

SELECT COUNT(*) 
FROM table AS t1 
JOIN table AS t2 ON t1.group_id=t2.group_id 
WHERE t1.user_id=1 AND t2.user_id=3; 

Answer 4

SELECT COUNT(*) 
FROM TABLE_NAME USER_ONE_INFO 
     TABLE_NAME USER_TWO_INFO 
WHERE USER_ONE_INFO.ID = USER_ONE_ID 
AND USER_TWO_INFO.ID = USER_TWO_ID 
AND USER_ONE_INFO.GROUP_ID = USER_TWO_INFO.GROUP_ID;