SQL Union只計算一個查詢

Question

我試圖計算表中的行。目前即時通訊使用此：

$sql = "SELECT COUNT(*) 
     FROM `friends` 
     WHERE `user1`='".$user1."' 
      AND `user2`='".$user2."' 
      AND `valid`=0 
     UNION 
     SELECT COUNT(*) 
     FROM `friends` 
     WHERE `user1`='".$user2."' 
      AND `user2`='".$user1."' 
      AND `valid`=0"; 

正如你看到的，user1既可以是$user1和$user2。但它不會計算UNION之後的行，它只會在UNION之前執行第一個查詢，所以即時結束時爲0，當我實際上應該計數1行時。

我該如何解決這個問題？

Answer 1

另一種選擇，這種替換查詢：

$sql = "SELECT COUNT(*) 
    FROM `friends` 
    WHERE (
      (`user1`='".$user1."' AND `user2`='".$user2."') OR 
      (`user1`='".$user2."' AND `user2`='".$user1."') 
     ) 
    AND `valid`=0"; 

Answer 2

改爲使用UNION ALL。 UNION將排除重複的行。

Answer 3

您的查詢實際上返回2個記錄 - 0爲第一計數和1第二。你可以使用一個子查詢到SUM()您的結果...

$sql = "SELECT SUM(A) AS COUNT FROM 
(SELECT COUNT(*) AS A 
     FROM `friends` 
     WHERE `user1`='".$user1."' 
      AND `user2`='".$user2."' 
      AND `valid`=0 
     UNION 
     SELECT COUNT(*) 
     FROM `friends` 
     WHERE `user1`='".$user2."' 
      AND `user2`='".$user1."' 
      AND `valid`=0 
)"; 

Answer 4

您可以使用一個更簡單的解決方案：

SELECT COUNT(*) 
FROM friends 
WHERE 
    $user1 IN (user1,user2) AND 
    $user2 IN (user1,user2) AND 
    valid = 0