合并两个mysql COUNT（*）结果，不同的列

Question

我正在尝试合并以下查询的计数：

  SELECT recipient AS otheruser, COUNT(*) 
    FROM privatemessages 
   WHERE sender = '$userid' 
GROUP BY recipient

  SELECT sender AS otheruser, COUNT(*) 
    FROM privatemessages 
   WHERE recipient = '$userid' 
GROUP BY sender

无论如何，如果要合并这两个查询，并为每个“ otheruser”将count（*）加在一起

Answer 1

最直接的方法是使用SUM / Condition

SELECT
     CASE WHEN sender = '$userid' THEN recipient else sender END AS OtherUser,
     SUM(sender = '$userid') AS RCount,
     SUM(recipient = '$userid') AS SCount,
     COUNT(*) total
FROM
     privatemessages 
WHERE
     '$userid' IN (sender , recipient )
GROUP BY
     OtherUser

演示

更新资料

感谢deltab和Michael Buen，我清理了SUM和GROUP BY语句

Answer 2

最直接的方法是只使用两个查询。
使用2个查询请求2个不同的数据集绝对没有害处，但使用一个查询执行此操作不是一个原因。

Answer 3

您可以像这样将它们与UNION结合使用：

SELECT otheruser, COUNT(*) FROM
(SELECT recipient AS otheruser
FROM privatemessages 
WHERE sender = '$userid' 
GROUP BY recipient
UNION
SELECT sender AS otheruser
FROM privatemessages 
WHERE recipient = '$userid' 
GROUP BY sender)

Answer 4

SELECT recipient AS r, sender AS s, COUNT(total) // can't use same alias
FROM privatemessages
WHERE sender = '$userid' AND recipient = '$userid'
GROUP BY s;

然后在您的结果函数中，调用计数

while ($row = $result) {
  echo $row['COUNT(total)'];
}

我相信此查询应能按预期工作。 原始文件唯一的问题是双重别名和两个不同字段的分组。 这可以在2个单独的查询中进行，但是结合起来就无法完成（至少是别名，对于GROUP BY则不这样认为）。

希望这对您有用。

更新

COUNT一个很好的选择是简单地使用num_rows ...。因此，上面的查询将是：

SELECT recipient AS r, sender AS s // can't use same alias
FROM privatemessages
WHERE s = '$userid' AND r = '$userid'
GROUP BY s;

然后在您的结果函数中，调用num_rows函数：

mysql_num_rows($result);