今天在利用DATE_FORMATE處理兩個(gè)日期判斷時(shí)發(fā)現(xiàn)提示 Illegal mix of collations (utf8_general_ci,COERCIBLE),這個(gè)是字符集問題呀,但我是日期怎么會(huì)這樣,當(dāng)時(shí)沒看到,后來看到一篇文章才想起來,下面我們一起來看看解決辦法.

處理一個(gè)SQL,簡(jiǎn)化過后的執(zhí)行報(bào)錯(cuò),代碼如下:

1. mysql> select date_format('2013-11-19','Y-m-d') > timediff('2013-11-19', '2013-11-20');                            
2.  
3. ERROR 1267 (HY000): Illegal mix of collations (utf8_general_ci,COERCIBLE) and (latin1_swedish_ci,NUMERIC) for operation '>' 

乍一看挺莫名其妙的,查了下手冊(cè),發(fā)現(xiàn)有這么一段:

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.

也就是說,DATE_FORMATE() 函數(shù)返回的結(jié)果是帶有字符集/校驗(yàn)集屬性的,而 TIMEDIFF() 函數(shù)則沒有字符集/校驗(yàn)集屬性,我們來驗(yàn)證一下,代碼如下:

1. mysql> set names utf8; 
2. mysql> select charset(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. +--------------------------------------------+-----------------------------------------------+ 
8.  
9. mysql> set names gb2312; 
10. mysql> select charset(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. +--------------------------------------------+-----------------------------------------------+//開源代碼Vevb.com 
14. | gb2312                                     | binary                                        | 
15. +--------------------------------------------+-----------------------------------------------+ 

可以看到,隨著通過 SET NAMES 修改 character_set_connection、collation_connection  值,DATE_FORMAT() 函數(shù)返回結(jié)果的字符集也跟著不一樣,在這種情況下,想要正常工作,就需要將結(jié)果進(jìn)行一次字符集轉(zhuǎn)換,代碼如下:

1. mysql> select date_format('2013-11-19','Y-m-d') > convert(timediff('2013-11-19', '2013-11-20') using utf8); 
2. +----------------------------------------------------------------------------------------------+ 
3. | date_format('2013-11-19','Y-m-d') > convert(timediff('2013-11-19', '2013-11-20') using utf8) | 
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,下面是函數(shù)的參數(shù)說明: