Mysql str_to_date 不执行任何操作

Question

我的数据库中有一个 varchar 类型的 datecreated 字段。不幸的是，我无法将此字段更改为日期格式，因此我必须在选择数据时执行此操作。我试图根据日期对记录进行排序(以便显示最近的年、月、日、小时、分钟、秒)。字段格式看起来像这样 dd-mm-yyyy hh:mm:ss ，所以在我的查询中，我正在尝试以下操作，但它完全没有排序:

SELECT * FROM submissions ORDER BY str_to_date(datecreated,'%d-%m-%Y %H:%i:%s') DESC

它所做的只是根据 id 字段显示记录...

Answer 1

假设所有 datecreated 值都与您指定的格式匹配，则该查询应该有效。

下面的示例显示您的查询在 MySQL 5.6.14 中使用过去 4 年分布的 10 个随机日期正常运行:

设置:

mysql> create table submissions (
    -> id int not null auto_increment primary key,
    -> datecreated varchar(20)
    -> );
Query OK, 0 rows affected (0.02 sec)

mysql> 
mysql> insert into submissions (datecreated) select date_format(now() - interval (rand() * 31536000 * 4) second,'%d-%m-%Y %H:%i:%s');
Query OK, 1 row affected (0.00 sec)
Records: 1  Duplicates: 0  Warnings: 0

mysql> insert into submissions (datecreated) select date_format(now() - interval (rand() * 31536000 * 4) second,'%d-%m-%Y %H:%i:%s');
Query OK, 1 row affected (0.00 sec)
Records: 1  Duplicates: 0  Warnings: 0

mysql> insert into submissions (datecreated) select date_format(now() - interval (rand() * 31536000 * 4) second,'%d-%m-%Y %H:%i:%s');
Query OK, 1 row affected (0.00 sec)
Records: 1  Duplicates: 0  Warnings: 0

mysql> insert into submissions (datecreated) select date_format(now() - interval (rand() * 31536000 * 4) second,'%d-%m-%Y %H:%i:%s');
Query OK, 1 row affected (0.00 sec)
Records: 1  Duplicates: 0  Warnings: 0

mysql> insert into submissions (datecreated) select date_format(now() - interval (rand() * 31536000 * 4) second,'%d-%m-%Y %H:%i:%s');
Query OK, 1 row affected (0.01 sec)
Records: 1  Duplicates: 0  Warnings: 0

mysql> insert into submissions (datecreated) select date_format(now() - interval (rand() * 31536000 * 4) second,'%d-%m-%Y %H:%i:%s');
Query OK, 1 row affected (0.00 sec)
Records: 1  Duplicates: 0  Warnings: 0

mysql> insert into submissions (datecreated) select date_format(now() - interval (rand() * 31536000 * 4) second,'%d-%m-%Y %H:%i:%s');
Query OK, 1 row affected (0.00 sec)
Records: 1  Duplicates: 0  Warnings: 0

mysql> insert into submissions (datecreated) select date_format(now() - interval (rand() * 31536000 * 4) second,'%d-%m-%Y %H:%i:%s');
Query OK, 1 row affected (0.00 sec)
Records: 1  Duplicates: 0  Warnings: 0

mysql> insert into submissions (datecreated) select date_format(now() - interval (rand() * 31536000 * 4) second,'%d-%m-%Y %H:%i:%s');
Query OK, 1 row affected (0.00 sec)
Records: 1  Duplicates: 0  Warnings: 0

mysql> insert into submissions (datecreated) select date_format(now() - interval (rand() * 31536000 * 4) second,'%d-%m-%Y %H:%i:%s');
Query OK, 1 row affected (0.00 sec)
Records: 1  Duplicates: 0  Warnings: 0

查询:

mysql> SELECT * FROM submissions ORDER BY str_to_date(datecreated,'%d-%m-%Y %H:%i:%s') DESC;
+----+---------------------+
| id | datecreated         |
+----+---------------------+
|  3 | 16-11-2013 10:36:23 |
| 10 | 23-03-2013 23:04:52 |
|  4 | 02-08-2012 08:02:59 |
|  1 | 13-06-2012 21:52:34 |
|  7 | 02-10-2011 05:59:49 |
|  9 | 22-07-2011 14:04:19 |
|  2 | 04-07-2011 03:09:08 |
|  8 | 03-06-2011 03:55:04 |
|  6 | 06-01-2011 20:50:50 |
|  5 | 05-01-2011 20:54:16 |
+----+---------------------+
10 rows in set (0.00 sec)