MySQL中日期比较时遇到的编码问题解决办法

2024-07-24 12:47:01

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今天帮同事处理一个SQL（简化过后的）执行报错：

复制代码代码如下:

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 '>'

乍一看挺莫名其妙的，查了下手册，发现有这么一段：
复制代码代码如下:

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：
复制代码代码如下:

mysql> set names utf8;
mysql> select charset(date_format('2013-11-19','Y-m-d')), charset(timediff('2013-11-19', '2013-11-20'));
+--------------------------------------------+-----------------------------------------------+
| charset(date_format('2013-11-19','Y-m-d')) | charset(timediff('2013-11-19', '2013-11-20')) |
+--------------------------------------------+-----------------------------------------------+
| utf8 | binary |
+--------------------------------------------+-----------------------------------------------+

mysql> set names gb2312;
mysql> select charset(date_format('2013-11-19','Y-m-d')), charset(timediff('2013-11-19', '2013-11-20'));
+--------------------------------------------+-----------------------------------------------+
| charset(date_format('2013-11-19','Y-m-d')) | charset(timediff('2013-11-19', '2013-11-20')) |
+--------------------------------------------+-----------------------------------------------+
| gb2312 | binary |
+--------------------------------------------+-----------------------------------------------+

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