Question

我试图计算表格中的行数。目前即时使用此：

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

如您所见，user1可以是$user1和$user2。但是它不计算UNION之后的行，它只会在UNION之前执行第一次查询，所以当我实际上应该计算1行时，我最终得到0。

我该如何解决这个问题？

Answer 1

另一种选择，用以下内容替换您的查询：

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

Answer 2

您的查询实际上会返回2条记录 - 第一次计数为0，第二次为1。您可以使用子查询SUM()您的结果...

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

Answer 3

请改用UNION ALL。 UNION将排除重复的行。

Answer 4

您可以使用更简单的解决方案：

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

SQL Union只计算一个查询

4 个答案: