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 程式師世界 >> 數據庫知識 >> MYSQL數據庫 >> MySQL綜合教程 >> MySQL中DATE_FORMATE函數應用時的留意點

MySQL中DATE_FORMATE函數應用時的留意點

編輯:MySQL綜合教程

MySQL中DATE_FORMATE函數應用時的留意點。本站提示廣大學習愛好者:(MySQL中DATE_FORMATE函數應用時的留意點)文章只能為提供參考,不一定能成為您想要的結果。以下是MySQL中DATE_FORMATE函數應用時的留意點正文


明天幫同事處置一個SQL(簡化事後的)履行報錯:

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 '>'

乍一看挺莫明其妙的,查了下手冊,發明有這麼一段:

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() 函數前往的成果是帶有字符集/校驗集屬性的,而 TIMEDIFF() 函數則沒有字符集/校驗集屬性,我們來驗證一下:

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                    |
+--------------------------------------------+-----------------------------------------------+

可以看到,跟著經由過程 SET NAMES 修正 character_set_connection、collation_connection  值,DATE_FORMAT() 函數前往成果的字符集也隨著紛歧樣。在這類情形下,想要正常任務,就須要將成果停止一次字符集轉換,例如:

mysql> select date_format('2013-11-19','Y-m-d') > convert(timediff('2013-11-19', '2013-11-20') using utf8);
+----------------------------------------------------------------------------------------------+
| date_format('2013-11-19','Y-m-d') > convert(timediff('2013-11-19', '2013-11-20') using utf8) |
+----------------------------------------------------------------------------------------------+
|                                              1 |
+----------------------------------------------------------------------------------------------+

便可以了 :)

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