合並兩個mysql COUNT（*）結果，不同的列

Question

我正在嘗試合並以下查詢的計數：

  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

無論如何，如果要合並這兩個查詢，並為每個“ otheruser”將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

更新資料

感謝deltab和Michael Buen，我清理了SUM和GROUP BY語句

Answer 2

最直接的方法是只使用兩個查詢。
使用2個查詢請求2個不同的數據集絕對沒有害處，但使用一個查詢執行此操作不是一個原因。

Answer 3

您可以像這樣將它們與UNION結合使用：

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;

然后在您的結果函數中，調用計數

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

我相信此查詢應能按預期工作。 原始文件唯一的問題是雙重別名和兩個不同字段的分組。 這可以在2個單獨的查詢中進行，但是結合起來就無法完成（至少是別名，對於GROUP BY則不這樣認為）。

希望這對您有用。

更新

COUNT一個很好的選擇是簡單地使用num_rows ...。因此，上面的查詢將是：

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

然后在您的結果函數中，調用num_rows函數：

mysql_num_rows($result);