mysql union group by_Mysql UNION和GROUP BY

我有2个表需要根据日期和2值加在一起.

这给了我所有信息的清单 – 罚款.

$query = (SELECT date, debit, credit , note FROM proj3_cash )

UNION

(SELECT settle, purch, sale, issue FROM proj3_trades)

ORDER BY date";

现在我需要从两个表中分组每日总计的信息.

$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";

好的,但是如果每张表中的日期相同,我得到：

date SUM(debit) SUM(credit)

--------------------------------------

-12-02 0.00 170.02

-12-02 296449.91 233111.10

如何将两人分成同一天？

如果我最后添加GROUP BY – 我只收到一个错误.还是应该用JOIN来完成？