MySQL日期字符串转换成NULL值的异常处理

1，YYYYmmdd格式日期转换为null

看如下记录，一个能取到值，一个取不到值**
mysql> SELECT DATE_FORMAT(STR_TO_DATE(‘20150922 13:01:01’, ‘%Y%m%d %H:%m:%s’),’%H:%m’);
±-------------------------------------------------------------------------+
| DATE_FORMAT(STR_TO_DATE(‘20150922 13:01:01’, ‘%Y%m%d %H:%m:%s’),’%H:%m’) |
±-------------------------------------------------------------------------+
| 13:01 |
±-------------------------------------------------------------------------+
1 row in set (0.00 sec)

mysql> SELECT DATE_FORMAT(STR_TO_DATE(‘20150922 12:55:00’, ‘%Y%m%d %H:%m:%s’),’%H:%m’);
±-------------------------------------------------------------------------+
| DATE_FORMAT(STR_TO_DATE(‘20150922 12:55:00’, ‘%Y%m%d %H:%m:%s’),’%H:%m’) |
±-------------------------------------------------------------------------+
| NULL |
±-------------------------------------------------------------------------+
1 row in set, 1 warning (0.00 sec)

mysql>

2，查看报错信息：

mysql> show warnings;
±--------±-----±-----------------------------------------------------------------------+
| Level | Code | Message |
±--------±-----±-----------------------------------------------------------------------+
| Warning | 1411 | Incorrect datetime value: ‘20150922 12:55:00’ for function str_to_date |
±--------±-----±-----------------------------------------------------------------------+
1 row in set (0.00 sec)

mysql>
报警说是Incorrect datetime value: ‘20150922 12:55:00’ for function str_to_date，不正确的日期格式，所以换成比较规范的日期格式

原blog地址：http://blog.youkuaiyun.com/mchdba/article/details/48719765，未经过csdn原博客博主mchdba允许，不能转载。

3，换成规范的%Y-%m-%d %H:%i:%s试试

mysql> select DATE_FORMAT(str_to_date(‘2015-09-22 13:00:01’, ‘%Y-%m-%d %H:%i:%s’),’%H:%i’);
±-----------------------------------------------------------------------------+
| DATE_FORMAT(str_to_date(‘2015-09-22 13:00:01’, ‘%Y-%m-%d %H:%i:%s’),’%H:%i’) |
±-----------------------------------------------------------------------------+
| 13:00 |
±-----------------------------------------------------------------------------+
1 row in set (0.00 sec)

mysql> select DATE_FORMAT(str_to_date(‘2015-09-22 12:55:00’, ‘%Y-%m-%d %H:%i:%s’),’%H:%i’);
±-----------------------------------------------------------------------------+
| DATE_FORMAT(str_to_date(‘2015-09-22 12:55:00’, ‘%Y-%m-%d %H:%i:%s’),’%H:%i’) |
±-----------------------------------------------------------------------------+
| 12:55 |
±-----------------------------------------------------------------------------+
1 row in set (0.00 sec)

mysql>

看到在规范的格式下，日期从字符串转换到日期格式，然后截取时分都是能取到值的。

参考官网地址：http://dev.mysql.com/doc/refman/5.6/en/date-and-time-functions.html#function_str-to-date

4，再次确定缩小范围，是%h的问题，将时换成大写就搞定了

再看到一个案例，将格式变成2015-09-22 13:00:01表准备格式，可以仍然取不到时分值，如下所示：

mysql> select DATE_FORMAT(str_to_date('2015-09-22 13:00:01', '%Y-%m-%d %h:%i:%s'),'%h:%i');
+------------------------------------------------------------------------------+
| DATE_FORMAT(str_to_date('2015-09-22 13:00:01', '%Y-%m-%d %h:%i:%s'),'%h:%i') |
+------------------------------------------------------------------------------+
| NULL                                                                         |
+------------------------------------------------------------------------------+
1 row in set, 1 warning (0.00 sec)

mysql> select DATE_FORMAT(str_to_date('2015-09-22 12:55:00', '%Y-%m-%d %h:%i:%s'),'%h:%i');
+------------------------------------------------------------------------------+
| DATE_FORMAT(str_to_date('2015-09-22 12:55:00', '%Y-%m-%d %h:%i:%s'),'%h:%i') |
+------------------------------------------------------------------------------+
| 12:55                                                                        |
+------------------------------------------------------------------------------+
1 row in set (0.00 sec)

mysql> 

那么问题在哪里呢？只能再次去官网找答案，找到http://dev.mysql.com/doc/refman/5.6/en/date-and-time-functions.html#function_get-format
看到终极标准格式为：’%Y-%m-%d %H.%i.%s’，换成这个试试，看到范例中的差异在哪里了吗？就在于%H和%h的区别啊，如下所示：

mysql> select DATE_FORMAT(str_to_date('20150922 13:00:01', '%Y%m%d %h:%i:%s'),'%h:%i');
+--------------------------------------------------------------------------+
| DATE_FORMAT(str_to_date('20150922 13:00:01', '%Y%m%d %h:%i:%s'),'%h:%i') |
+--------------------------------------------------------------------------+
| NULL                                                                     |
+--------------------------------------------------------------------------+
1 row in set, 1 warning (0.00 sec)

mysql> select DATE_FORMAT(str_to_date('20150922 12:55:00', '%Y%m%d %h:%i:%s'),'%h:%i');
+--------------------------------------------------------------------------+
| DATE_FORMAT(str_to_date('20150922 12:55:00', '%Y%m%d %h:%i:%s'),'%h:%i') |
+--------------------------------------------------------------------------+
| 12:55                                                                    |
+--------------------------------------------------------------------------+
1 row in set (0.00 sec)

mysql> 

然后标准的日期格式为：%Y%m%d %H:%i:%s’或者%Y-%m-%d %H:%i:%s’ 都可以的，如下所示：

select DATE_FORMAT(str_to_date(‘20150922 13:00:01’, ‘%Y%m%d %H:%i:%s’),’%H:%i’);
select DATE_FORMAT(str_to_date(‘20150922 12:55:00’, ‘%Y%m%d %H:%i:%s’),’%H:%i’);