Mysql UNION 和 GROUP BY

Question

我需要根据日期和 2 个值将 2 个表加在一起。

这给了我所有信息的列表 - 很好。

$query = (SELECT  date, debit, credit , note  FROM proj3_cash )
UNION 
(SELECT  settle, purch, sale, issue FROM proj3_trades)
ORDER BY date";

现在我需要对两张表中的每日总计信息进行 GROUP。

$query = "(SELECT  date, SUM(debit), SUM(credit)FROM proj3_cash  GROUP BY date)
UNION 
(SELECT  settle as date, SUM(purch) as debit, SUM(sale) as credit FROM proj3_trades GROUP BY date)
ORDER BY date";

很好，但是如果每个表中有相同日期的内容，我会得到：

date        SUM(debit)    SUM(credit)
--------------------------------------
2010-12-02  0.00          170.02 
2010-12-02  296449.91     233111.10 

如何将两者归为同一天？

如果我在最后添加 GROUP BY - 我只会收到错误消息。还是应该通过 JOIN 来完成？

Answer 1

您可以使用派生表实现此目的：

SELECT date, SUM(debit), SUM(credit)
FROM
(
    SELECT  date, debit, credit
      FROM proj3_cash
    UNION ALL
    SELECT  settle as date, 
            purch as debit, 
            sale as credit 
      FROM proj3_trades
) derivedTable
GROUP BY date
ORDER BY date

我已将 UNION 更改为 UNION ALL，因为 union 将消除两个表中的重复项。