选择每个月的最后一天？

Question

我在MySQL中有以下数据：

+------------+-------+
| myDATE     | delta |
+------------+-------+
| 2015-08-29 |    12 |
| 2015-08-30 |    12 |
| 2015-08-31 |    10 |
| 2015-09-01 |     0 |
| 2015-09-02 |  0.15 |
+------------+-------+

我想运行一个查询，选择每个月的最后一天并显示数据。我以为我有它工作，但它没有显示昨天的数据。

select mydate, delta from data group by date_format(mydate, '%Y-%m');

结果：

+------------+-------+
| mydate     | delta |
+------------+-------+
| 2015-08-29 |    12 |
| 2015-09-01 |     0 |
+------------+-------+

我错过了什么？

我正在寻找它来回复:(即每个月的最后一天有记录）

+------------+-------+
| myDATE     | delta |
+------------+-------+
| 2015-08-31 |    10 |
| 2015-09-02 |  0.15 |
+------------+-------+

Answer 1

select last_day(mydate), sum(delta) from data group by last_day(mydate)

last_day是一个函数，它返回给定日期的月份的最后一天

https://dev.mysql.com/doc/refman/5.5/en/date-and-time-functions.html#function_last-day

回答更新后的问题

select data.`myDate`, data.delta from data inner join
(select max(`myDate`) myDate from data group by date_format(mydate, '%Y-%m')) a
on a.myDate = data.myDate