mysql資料庫中查詢時間

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項目中要對資料按時間處理，在資料庫中，時間處理的格式如

2014-12-09 06:30:17

時間查詢出來如下所示：

現在要查詢具體有哪天的資料，應用substring函數，SQL如下：

select distinct substring(( start_time ) from 1 for 10) as t from perf_service_msg;

查詢結果如下：

+------------+| t          |+------------+| 2014-12-08 || 2014-12-05 || 2014-11-20 || 2014-12-02 || 2014-12-07 || 2014-12-06 || 2014-12-03 || 2014-12-04 || 2014-11-21 |+------------+9 rows in set

MYSQL中SUBSTRING的說明：

 SUBSTR(str,pos), SUBSTR(str FROM pos), SUBSTR(str,pos,len), SUBSTR(str FROM pos FOR len)SUBSTR() is a synonym for SUBSTRING(). SUBSTRING(str,pos), SUBSTRING(str FROM pos), SUBSTRING(str,pos,len), SUBSTRING(str FROM pos FOR len)The forms without a len argument return a substring from string str starting at position pos. The forms with a len argument return a substring len characters long from string str, starting at position pos. The forms that use FROM are standard SQL syntax. It is also possible to use a negative value for pos. In this case, the beginning of the substring is pos characters from the end of the string, rather than the beginning. A negative value may be used for pos in any of the forms of this function.For all forms of SUBSTRING(), the position of the first character in the string from which the substring is to be extracted is reckoned as 1.mysql> SELECT SUBSTRING(‘Quadratically‘,5);        -> ‘ratically‘mysql> SELECT SUBSTRING(‘foobarbar‘ FROM 4);        -> ‘barbar‘mysql> SELECT SUBSTRING(‘Quadratically‘,5,6);        -> ‘ratica‘mysql> SELECT SUBSTRING(‘Sakila‘, -3);        -> ‘ila‘mysql> SELECT SUBSTRING(‘Sakila‘, -5, 3);        -> ‘aki‘mysql> SELECT SUBSTRING(‘Sakila‘ FROM -4 FOR 2);        -> ‘ki‘This function is multibyte safe.If len is less than 1, the result is the empty string.

參考：http://dev.mysql.com/doc/refman/5.0/en/string-functions.html#function_substr

 

mysql資料庫中查詢時間