Question

这感觉它应该很容易，但我无法得到它而且我已经尝试了所有东西。

我如何只获取此查询返回的行数：

(SELECT Alias1 . *, 
        Alias2 . * 
 FROM   Table1 AS Alias1 
        LEFT JOIN Table2 AS Alias2 USING ( Col1 ) 
 WHERE  Alias1.Col1 != 'blah1' 
        AND Alias1.Col2 LIKE 'blah2' 
        AND ( Alias1.Col3 LIKE 'blah3' 
               OR Alias1.Col3 LIKE 'blah4' ) 
        AND Alias1.Col4 = 'blah5' 
        AND Alias2.Col7 LIKE 'blah6' 
 ORDER  BY Alias1.Col6 DESC 
 LIMIT  50) 

UNION 

(SELECT Alias1 . *, 
        Alias2 . * 
 FROM   Table1 AS Alias1 
        LEFT JOIN Table2 AS Alias2 USING ( Col1 ) 
 WHERE  Alias1.Col1 != 'blah1' 
        AND Alias1.Col2 LIKE 'blah2' 
        AND ( Alias1.Col3 LIKE 'blah3' 
               OR Alias1.Col3 LIKE 'blah4' ) 
        AND Alias1.Col4 = 'blah5' 
        AND Alias2.Col5 LIKE 'blah6' 
 ORDER  BY Alias1.Col6 DESC 
 LIMIT  50) 

UNION 

(SELECT Alias1 . *, 
        Alias2 . * 
 FROM   Table1 AS Alias1 
        LEFT JOIN Table2 AS Alias2 USING ( Col1 ) 
 WHERE  Alias1.Col1 != 'blah1' 
        AND Alias1.Col2 LIKE 'blah2'
        AND ( Alias1.Col3 LIKE 'blah3' 
               OR Alias1.Col3 LIKE 'blah4' ) 
        AND Alias1.Col4 = 'blah5' 
 ORDER  BY Alias1.Col6 DESC 
 LIMIT  50)

我想我可以使用PHP执行查询，然后对结果执行mysql_num_rows，但我想直接使用SQL，因为我听说它节省了一步更快。

谢谢！

编辑：

以下是给我错误（＃1060 - 重复列名'Col1'）：

   SELECT COUNT(*) FROM (
   (SELECT Alias1 . *, 
            Alias2 . * 
     FROM   Table1 AS Alias1 
            LEFT JOIN Table2 AS Alias2 USING ( Col1 ) 
     WHERE  Alias1.Col1 != 'blah1' 
            AND Alias1.Col2 LIKE 'blah2' 
            AND ( Alias1.Col3 LIKE 'blah3' 
                   OR Alias1.Col3 LIKE 'blah4' ) 
            AND Alias1.Col4 = 'blah5' 
            AND Alias2.Col7 LIKE 'blah6' 
     ORDER  BY Alias1.Col6 DESC 
     LIMIT  50) 

    UNION 

    (SELECT Alias1 . *, 
            Alias2 . * 
     FROM   Table1 AS Alias1 
            LEFT JOIN Table2 AS Alias2 USING ( Col1 ) 
     WHERE  Alias1.Col1 != 'blah1' 
            AND Alias1.Col2 LIKE 'blah2' 
            AND ( Alias1.Col3 LIKE 'blah3' 
                   OR Alias1.Col3 LIKE 'blah4' ) 
            AND Alias1.Col4 = 'blah5' 
            AND Alias2.Col5 LIKE 'blah6' 
     ORDER  BY Alias1.Col6 DESC 
     LIMIT  50) 

    UNION 

    (SELECT Alias1 . *, 
            Alias2 . * 
     FROM   Table1 AS Alias1 
            LEFT JOIN Table2 AS Alias2 USING ( Col1 ) 
     WHERE  Alias1.Col1 != 'blah1' 
            AND Alias1.Col2 LIKE 'blah2'
            AND ( Alias1.Col3 LIKE 'blah3' 
                   OR Alias1.Col3 LIKE 'blah4' ) 
            AND Alias1.Col4 = 'blah5' 
     ORDER  BY Alias1.Col6 DESC 
     LIMIT  50)
   ) a

以下是给我错误（＃1064 - 您的SQL语法中有错误;）：

 SELECT COUNT(*) FROM (
   (SELECT Alias1 . *, 
            Alias2 . * 
     FROM   Table1 AS Alias1 
            LEFT JOIN Table2 AS Alias2 USING ( Col1 ) 
     WHERE  Alias1.Col1 != 'blah1' 
            AND Alias1.Col2 LIKE 'blah2' 
            AND ( Alias1.Col3 LIKE 'blah3' 
                   OR Alias1.Col3 LIKE 'blah4' ) 
            AND Alias1.Col4 = 'blah5' 
            AND Alias2.Col7 LIKE 'blah6' 
     ORDER  BY Alias1.Col6 DESC 
     LIMIT  50) a

    UNION 

    (SELECT Alias1 . *, 
            Alias2 . * 
     FROM   Table1 AS Alias1 
            LEFT JOIN Table2 AS Alias2 USING ( Col1 ) 
     WHERE  Alias1.Col1 != 'blah1' 
            AND Alias1.Col2 LIKE 'blah2' 
            AND ( Alias1.Col3 LIKE 'blah3' 
                   OR Alias1.Col3 LIKE 'blah4' ) 
            AND Alias1.Col4 = 'blah5' 
            AND Alias2.Col5 LIKE 'blah6' 
     ORDER  BY Alias1.Col6 DESC 
     LIMIT  50) b

    UNION 

    (SELECT Alias1 . *, 
            Alias2 . * 
     FROM   Table1 AS Alias1 
            LEFT JOIN Table2 AS Alias2 USING ( Col1 ) 
     WHERE  Alias1.Col1 != 'blah1' 
            AND Alias1.Col2 LIKE 'blah2'
            AND ( Alias1.Col3 LIKE 'blah3' 
                   OR Alias1.Col3 LIKE 'blah4' ) 
            AND Alias1.Col4 = 'blah5' 
     ORDER  BY Alias1.Col6 DESC 
     LIMIT  50) c
   ) z

Answer 1

将整个查询包装在括号中（使其成为子查询）并从中执行选择计数（*）：

select count(*) from (YOUR HUGE QUERY UNION YOUR HUGE QUERY) a

Answer 2

将整个查询包装为

SELECT COUNT(*) FROM (<Your query>)

Answer 3

真的使用mysql_num_rows。对于联合，数据库无论如何都需要构建一个临时表，这是代价高昂的事情。即使可以在SQL中直接执行，也不会通过要求MySQL给你这个数字来节省很多。

无论如何，只要使用mysql_num_rows函数，数据就不会发送给PHP。

Answer 4

您需要为列Col1指定一个唯一的别名，因为它在join中使用，需要唯一的列才能相互匹配。如果遇到重复的列，它将抛出错误1060。检查一下：Duplicate column names in SQL query

在您的情况下，MySQL与表1和表2中的Col1混淆，从而导致错误。使用完毕后，您可以SELECT COUNT(*) from YourQuery

Answer 5

您需要为列Col1指定一个唯一的别名，因为它在join中使用，需要唯一的列才能相互匹配。如果遇到重复的列，它将抛出错误1060。检查一下：Duplicate column names in SQL query

在您的情况下，MySQL与表1和表2中的Col1混淆，从而导致错误。使用完毕后，您可以SELECT COUNT(*) from YourQuery

MySQL：如何计算复杂查询返回的行数

5 个答案: