为什么CAST()函数返回错误的日期？

Question

我试图从时间戳字段获取日期部分.我用过这个SQL查询:

select timestamp, CAST(timestamp as date) as date from messages

我得到了以下结果:

--------------------------------------------
|        timestamp        |      date      |
--------------------------------------------
|   2016-05-15 10:22:54   |   2016-05-16   |
--------------------------------------------

如上所示,生成的日期字段返回错误的日期,2016-05-16而原始日期是2016-05-15.

我们如何解决这个问题？

Answer 1

那不是问题!!! 它只设置了错误的time_zone.看样品

获取当前time_zone

SHOW GLOBAL VARIABLES LIKE 'time_zone'; -- systemwide setting
SHOW VARIABLES LIKE 'time_zone'; -- session setting

样品

MariaDB [mysql]> select t, CAST(t as date) FROM groupme LIMIT 1;
+---------------------+-----------------+
| t                   | CAST(t as date) |
+---------------------+-----------------+
| 2016-05-15 20:22:54 | 2016-05-15      |
+---------------------+-----------------+
1 row in set (0.00 sec)

MariaDB [mysql]> SET  time_zone ='-12:00';
Query OK, 0 rows affected (0.00 sec)

MariaDB [mysql]> select t, CAST(t as date) FROM groupme LIMIT 1;
+---------------------+-----------------+
| t                   | CAST(t as date) |
+---------------------+-----------------+
| 2016-05-14 20:22:54 | 2016-05-14      |
+---------------------+-----------------+
1 row in set (0.00 sec)

MariaDB [mysql]>

Answer 2

使用未投出日期,因为不是投射而是格式

select timestamp, date(timestamp) as my_date from messages

Answer 3

我建议您使用DATE_FORMAT函数而不是CAST,因为您要格式化日期

SELECT `timestamp`, DATE_FORMAT(`timestamp`, '%Y-%m-%d) as my_date from messages

另请注意,CAST和DATE函数都在内部调用Item_date_typecast函数,因此它们之间没有这种差异.