MySQL 里面的Where 和Having和Count 和distinct和Group By对比

mysql> select accid as uid,date(datetime) AS datetime from game.logLogin GROUP BY accid HAVING datetime='2013-8-20';
+---------+------------+
| uid     | datetime   |
+---------+------------+
|  | -- |
|  | -- |
+---------+------------+
 rows in set (0.00 sec)

而实际的例子是

mysql> select accid as uid,date(datetime) AS datetime from game.logLogin HAVING datetime='2013-8-20';
+---------+------------+
| uid     | datetime   |
+---------+------------+
|  | -- |
|  | -- |
|  | -- |
|  | -- |
|  | -- |
|  | -- |
|  | -- |
|  | -- |
|  | -- |
|  | -- |
|  | -- |
|  | -- |
|  | -- |
|  | -- |
|  | -- |
|        | -- |
|  | -- |
+---------+------------+
 rows in set (0.00 sec)

用大腿想都会不对

mysql> select distinct accid as uid from (select accid,date(datetime) AS datetime from game.logLogin HAVING datetime='2013-8-20') as t;
+---------+
| uid     |
+---------+
|  |
|  |
|  |
|  |
|  |
|  |
|  |
|  |
|        |
+---------+
 rows in set (0.00 sec)

当然如何不用 HAVING 和 DISTINCT 和 COUNT 还有GROUP By 的话是可以找出记录的

mysql> select accountID as uid,date(signTime) AS signTime from platform.account HAVING signTime='2013-8-20';
+---------+------------+
| uid     | signTime   |
+---------+------------+
|  | -- |
|  | -- |
+---------+------------+
 rows in set (0.00 sec)

mysql> select accountID as uid,date(signTime) AS signTime from platform.account HAVING signTime='2013-8-19';
+---------+------------+
| uid     | signTime   |
+---------+------------+
|  | -- |
|  | -- |
|  | -- |
|  | -- |
|  | -- |
|  | -- |
|  | -- |
|  | -- |
|  | -- |
|  | -- |
|  | -- |
|  | -- |
|  | -- |
+---------+------------+
 rows in set (0.00 sec)