Question

我对如何在一个查询中减去子查询提出了挑战。我不知道这是否可行或是否有办法绕过它。我感谢任何帮助，我可以得到。感谢。

 $query = SELECT name, email, (SELECT SUM(tx_amount) FROM #__tx WHERE (tx_from = id
 AND tx_from_code = code AND tx_type1 = 'Credit' AND tx_status = 'Approved') OR 
(tx_to = id AND tx_to_code = code AND tx_type2 = 'Credit' AND tx_status = 'Approved')) as Wallet_Balance, 
(SELECT SUM(tx_amount) FROM #__tx WHERE (tx_from = id AND tx_from_code = code AND 
tx_type1 = 'Debit' AND tx_status = 'Approved') OR (tx_to = id AND tx_to_code = code AND 
tx_type2 = 'Debit' AND tx_status = 'Approved')) as Wallet_Balancee, (Wallet_Balance-Wallet_Balancee) as Total FROM users WHERE id = '$id');

我一直收到错误未知列＆＃39; Wallet_Balance＆＃39;在＆＃39;字段列表＆＃39; 请帮忙。感谢

Answer 1

这是您的查询。问题很简单。您不能在同一select子句中使用列别名。

SELECT name, email,
       (SELECT SUM(tx_amount)
        FROM #__tx
        WHERE (tx_from = id AND tx_from_code = code AND
               tx_type1 = 'Credit' AND tx_status = 'Approved'
              ) OR 
              (tx_to = id AND tx_to_code = code AND
               tx_type2 = 'Credit' AND tx_status = 'Approved'
              )
       ) as Wallet_Balance, 
       (SELECT SUM(tx_amount)
        FROM #__tx
        WHERE (tx_from = id AND tx_from_code = code AND 
               tx_type1 = 'Debit' AND tx_status = 'Approved'
              ) OR
              (tx_to = id AND tx_to_code = code AND 
               tx_type2 = 'Debit' AND tx_status = 'Approved'
              )
       )  as Wallet_Balancee,
      (Wallet_Balance-Wallet_Balancee) as Total
FROM users
WHERE id = '$id';

您有几种选择。最简单的可能就是使用子查询：

SELECT name, email, Wallet_Balance, Wallet_Balancee,
       (Wallet_Balance-Wallet_Balancee) as Total
FROM (SELECT name, email,
             (SELECT SUM(tx_amount)
              FROM #__tx
              WHERE (tx_from = id AND tx_from_code = code AND
                     tx_type1 = 'Credit' AND tx_status = 'Approved'
                    ) OR 
                    (tx_to = id AND tx_to_code = code AND
                     tx_type2 = 'Credit' AND tx_status = 'Approved'
                    )
             ) as Wallet_Balance, 
             (SELECT SUM(tx_amount)
              FROM #__tx
              WHERE (tx_from = id AND tx_from_code = code AND 
                     tx_type1 = 'Debit' AND tx_status = 'Approved'
                    ) OR
                    (tx_to = id AND tx_to_code = code AND 
                     tx_type2 = 'Debit' AND tx_status = 'Approved'
                    )
             )  as Wallet_Balancee
      FROM users
      WHERE id = '$id';
     ) w;

您只为一个用户选择数据，因此创建派生表的开销非常小。

在查询中减去2个子查询

1 个答案: