MySQL查询：按天显示条目数

Question

我有一张结构表：

id|name|       date
---------------------------
 1|qwer|2011-08-29 13:11:59
 2|wert|2011-08-29 13:11:59
 3|erty|2011-08-30 13:11:59
 4|rtyu|2011-08-31 13:11:59

我需要一个查询来显示这样的数据：

    day   |number_of_entries
----------------------------
2011-08-29|                2
2011-08-30|                1
2011-08-31|                1

Answer 1

使用GROUP BY函数和COUNT函数提供以下内容：

SELECT DATE(`date`), COUNT(*) AS number_of_entires
FROM tablename
GROUP BY DATE(`date`)
ORDER BY `date`

GROUP BY - MySQL Reference Manual

DATE - MySQL Reference Manual

Answer 2

SELECT   DATE(`date`) AS day,
         COUNT(*)     AS number_of_entries
FROM     mytable
GROUP BY DATE(`date`)

使用MySQL的DATE()功能。