Question

有3个表：events，eventClients和clients。

编写一个查询，查找所有客户都有权访问的事件？

内部联接并不保证表中的所有行都参与，因此这没有帮助：

select * from events e
inner join eventclients ec on e.id = ec.eventid
inner join clients c on etc.clientid = c.id

Answer 1

您可以使用嵌套NOT EXISTS来检查：

SELECT e.* 
FROM   events e 
WHERE NOT EXISTS(
    SELECT 1 FROM  client c 
    WHERE NOT EXISTS(
        SELECT 1 FROM eventclients ec 
        WHERE ec.eventid = e.id AND c.id= ec.clientid 
    )
)

Demo

Answer 2

您也可以

SELECT e.id, e.name
  FROM events e LEFT JOIN eventclients ec
    ON e.id = ec.eventid LEFT JOIN clients c
    ON ec.clientid = c.id
 GROUP BY e.id, e.name
HAVING COUNT(ec.clientid) = 
(
  SELECT COUNT(*) FROM clients
)

这是 SQLFiddle 演示

Answer 3

假设您的意思是事件与客户端有多对多的关系， event_client 是它们之间的桥接表，那么你是否有任何其他问题要求跨多对多关系进行SQL连接。

SQL many to many select

How to filter SQL results in a has-many-through relation

如何编写Sql查询以查找另一个表中的所有参与行？

3 个答案: