MySQL中DATE_FORMATE函数内置字符集解析

今天在利用DATE_FORMATE处理两个日期判断时发现提示 Illegal mix of collations (utf8_general_ci,COERCIBLE),这个是字符集问题呀,但我是日期怎么会这样,当时没看到,后来看到一篇文章才想起来,下面我们一起来看看解决办法.

处理一个SQL,简化过后的执行报错,代码如下:

1. mysql>selectdate_format('2013-11-19','Y-m-d')>timediff('2013-11-19','2013-11-20');
3. ERROR1267(HY000):Illegalmixofcollations(utf8_general_ci,COERCIBLE)and(latin1_swedish_ci,NUMERIC)foroperation'>'

乍一看挺莫名其妙的,查了下手册,发现有这么一段:

The language used for day and month names and abbreviations is controlled by the value of the lc_time_names system variable (Section 9.7, “MySQL Server Locale Support”).

The DATE_FORMAT() returns a string with a character set and collation given by character_set_connection and collation_connection so that it can return month and weekday names containing non-ASCII characters.

也就是说,DATE_FORMATE() 函数返回的结果是带有字符集/校验集属性的,而 TIMEDIFF() 函数则没有字符集/校验集属性,我们来验证一下,代码如下:

1. mysql>setnamesutf8;
2. mysql>selectcharset(date_format('2013-11-19','Y-m-d')),charset(timediff('2013-11-19','2013-11-20'));
3. +--------------------------------------------+-----------------------------------------------+
4. |charset(date_format('2013-11-19','Y-m-d'))|charset(timediff('2013-11-19','2013-11-20'))|
5. +--------------------------------------------+-----------------------------------------------+
6. |utf8|binary|
7. +--------------------------------------------+-----------------------------------------------+
9. mysql>setnamesgb2312;
10. mysql>selectcharset(date_format('2013-11-19','Y-m-d')),charset(timediff('2013-11-19','2013-11-20'));
11. +--------------------------------------------+-----------------------------------------------+
12. |charset(date_format('2013-11-19','Y-m-d'))|charset(timediff('2013-11-19','2013-11-20'))|
13. +--------------------------------------------+-----------------------------------------------+//开源代码phpfensi.com
14. |gb2312|binary|
15. +--------------------------------------------+-----------------------------------------------+

可以看到,随着通过 SET NAMES 修改 character_set_connection、collation_connection 值,DATE_FORMAT() 函数返回结果的字符集也跟着不一样,在这种情况下,想要正常工作,就需要将结果进行一次字符集转换,代码如下:

1. mysql>selectdate_format('2013-11-19','Y-m-d')>convert(timediff('2013-11-19','2013-11-20')usingutf8);
2. +----------------------------------------------------------------------------------------------+
3. |date_format('2013-11-19','Y-m-d')>convert(timediff('2013-11-19','2013-11-20')usingutf8)|
4. +----------------------------------------------------------------------------------------------+
5. |1|
6. +----------------------------------------------------------------------------------------------+

就可以了.

P.S,MySQL的版本：5.5.20-55-log Percona Server (GPL), Release rel24.1,Revision 217.

附后,下面是函数的参数说明: