今天帮同事处理一个SQL(简化过后的)执行报错:
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mysql> select date_format( '2013-11-19' , 'Y-m-d' ) > timediff( '2013-11-19' , '2013-11-20' );
ERROR 1267 (HY000): Illegal mix of collations (utf8_general_ci,COERCIBLE) and (latin1_swedish_ci, NUMERIC ) for operation '>'
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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:
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mysql> set names utf8;
mysql> select charset(date_format( '2013-11-19' , 'Y-m-d' )), charset(timediff( '2013-11-19' , '2013-11-20' ));
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| charset(date_format( '2013-11-19' , 'Y-m-d' )) | charset(timediff( '2013-11-19' , '2013-11-20' )) |
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| utf8 | binary |
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mysql> set names gb2312;
mysql> select charset(date_format( '2013-11-19' , 'Y-m-d' )), charset(timediff( '2013-11-19' , '2013-11-20' ));
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| charset(date_format( '2013-11-19' , 'Y-m-d' )) | charset(timediff( '2013-11-19' , '2013-11-20' )) |
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| gb2312 | binary |
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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,例如:
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mysql> select date_format( '2013-11-19' , 'Y-m-d' ) > convert (timediff( '2013-11-19' , '2013-11-20' ) using utf8);
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| date_format( '2013-11-19' , 'Y-m-d' ) > convert (timediff( '2013-11-19' , '2013-11-20' ) using utf8) |
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就可以了 :)
(责任编辑:IT) |