Question

我有两张桌子：

表格消息（保留消息的创建者和消息）
id - creatorId - msg

和表message_viewers（告诉谁可以读取消息msgId）
msgId - userId

如果我以用户1创建消息并将其发送给用户2和用户3，则表格如下所示：

tbl_message:  
1 - 1 - 'message'
tbl_message_viewers:  
1 - 2  
1 - 3

我想要做的是获取用户x1 ... xN（任意数量的用户）之间的消息以及它们之间的消息。
（例如，如果用户是1,2和3，我想要创建者为1,2或3的消息，创建者的用户为2,3，创建者的用户为1,2和1，为2 creator = 3）
我不感兴趣来自1和2，或2和3，或1和3之间的消息，但仅限于3人之间的消息。

我尝试了不同的方法，例如在消息ID上加入两个表，选择creatorId IN（X，Y）的消息，然后只选择userId IN（X，Y）的行。也许关于分组和计算行的事情，但我无法找到一种方法来做这个工作。

编辑：SQL小提琴

http://sqlfiddle.com/#!2/963c0/1

Answer 1

我认为这可能会做你想要的：

SELECT m.*
FROM message m
INNER JOIN message_viewers mv ON m.id = mv.msgId
WHERE m.creatorId IN (1, 2, 3)
  AND mv.userId IN (1, 2, 3)
  AND NOT EXISTS (
    SELECT 1
    FROM message_viewers mv2
    WHERE mv2.msgId = mv.msgId
      AND mv2.userId NOT IN (1, 2, 3)
    )
  AND mv.userId != m.creatorId;

IN将为创建/可以看到的用户提供，mv.userId != m.creatorId用于从message_viewers表中排除创建者（如您在要求中所示）。

编辑：

由于只需要在这3个id之间发送消息，我想出了以下内容：

SELECT m.id,m.creatorId,m.message
FROM message m
INNER JOIN message_viewers mv ON m.id = mv.msgId
WHERE m.creatorId IN (1, 2, 3)
  AND mv.userId IN (1, 2, 3)
  AND mv.userId != m.creatorId
  AND NOT EXISTS (
    SELECT 1
    FROM message_viewers mv2
    WHERE mv2.msgId = mv.msgId
      AND mv2.userId NOT IN (1, 2, 3)
    )
GROUP BY 1,2,3
HAVING COUNT(*) = 2;

sqlfiddle demo

Answer 2

尝试使用join和IN（）子句

SELECT * FROM 
tbl_message m
JOIN tbl_message_viewers mv (m.id = mv.msgId )
WHERE m.creatorId IN(1,2,3) AND mv.userId IN(1,2,3)

Answer 3

听起来您可能想要BETWEEN运营商：

SELECT * FROM tablename WHERE fieldname BETWEEN 1 AND 10;
-- returns fieldname 1-10

但是，在这种情况下，BETWEEN具有包容性，因此您还需要指定!=这些条件：

SELECT * FROM tablename WHERE fieldname BETWEEN 1 AND 10 AND fieldname NOT IN (1, 10)
-- returns fieldname 2-9

http://www.w3schools.com/sql/sql_between.asp

Answer 4

这适用于oracle

首次加入会为我们不感兴趣的人获取行数第二次加入获取我们感兴趣的人的行数

in子句需要由某种动态sql生成还需要以某种方式生成number_of_people。

select msgId, count_1, count_2
  from message tm
       join ( select ty.msgId as ty_msgId, 
                     count(ty.msgId) as count_1 
                from message_viewers ty
               where ty.userId not in (:a,:b,:c)
            group by ty.msgId)
         on msgId = ty_msgId
       join (select tz.msgId as tz_msgId, 
                    count(tz.msgId) as count_2 
               from message_viewers tz
              where tz.userId in (:a,:b,:c)
              group by tz.msgId)
         on msgId = tz_msgId
      where createrId in(:a,:b,:c)
        and count_1 = 0
        and count_2 = :number_of_people -1;

我的sql更喜欢这个

select msgId, count_1, count_2
  from message tm
       left join ( select ty.msgId as ty_msgId, 
                     count(ty.msgId) as count_1 
                from message_viewers ty
               where ty.userId not in (:a,:b,:c)
            group by ty.msgId) as X
         on msgId = ty_msgId
       left join (select tz.msgId as tz_msgId, 
                    count(tz.msgId) as count_2 
               from message_viewers tz
              where tz.userId in (:a,:b,:c)
              group by tz.msgId) as Y
         on msgId = tz_msgId
      where createrId in(:a,:b,:c)
        and (count_1 = 0 or count_1 is null)
        and count_2 = :number_of_people -1;

MYSQL：查找特定用户之间的所有帖子

4 个答案: