MySQL 如何按日期排序但将空日期放在末尾

使用ORDER BY子句和IS NULL属性按日期排序并将空日期放在末尾，语法如下：

SELECT *FROM yourTableName
ORDER BY (yourDateColumnName IS NULL), yourDateColumnName DESC;

在上面的语法中，我们将首先对NULL进行排序，然后对日期进行排序。为了理解上面的语法，让我们先创建一个表。创建表的查询语句如下：

mysql> create table DateColumnWithNullDemo
   -> (
   -> Id int NOT NULL AUTO_INCREMENT,
   -> LoginDateTime datetime,
   -> PRIMARY KEY(Id)
   -> );
Query OK, 0 rows affected (0.84 sec)

使用插入命令在表中插入一些记录。查询语句如下：

mysql> insert into DateColumnWithNullDemo(LoginDateTime) values(date_add(now(),interval -1 year));
Query OK, 1 row affected (0.15 sec)
mysql> insert into DateColumnWithNullDemo(LoginDateTime) values(NULL);
Query OK, 1 row affected (0.17 sec)
mysql> insert into DateColumnWithNullDemo(LoginDateTime) values(NULL);
Query OK, 1 row affected (0.12 sec)
mysql> insert into DateColumnWithNullDemo(LoginDateTime) values(now());
Query OK, 1 row affected (0.18 sec)
mysql> insert into DateColumnWithNullDemo(LoginDateTime) values(curdate());
Query OK, 1 row affected (0.23 sec)
mysql> insert into DateColumnWithNullDemo(LoginDateTime) values('2017-08-25 15:30:35');
Query OK, 1 row affected (0.14 sec)
mysql> insert into DateColumnWithNullDemo(LoginDateTime) values(NULL);
Query OK, 1 row affected (0.15 sec)
mysql> insert into DateColumnWithNullDemo(LoginDateTime) values('2016-12-25 16:55:55');
Query OK, 1 row affected (0.15 sec)
mysql> insert into DateColumnWithNullDemo(LoginDateTime) values(NULL);
Query OK, 1 row affected (0.22 sec)
mysql> insert into DateColumnWithNullDemo(LoginDateTime) values('2014-11-12 10:20:23');
Query OK, 1 row affected (0.14 sec)
mysql> insert into DateColumnWithNullDemo(LoginDateTime) values('2020-01-01 06:45:23');
Query OK, 1 row affected (0.23 sec)

使用select语句从表中显示所有记录。查询语句如下：

mysql> select *from DateColumnWithNullDemo;

以下是输出结果：

+----+---------------------+
| Id | LoginDateTime       |
+----+---------------------+
|  1 | 2018-01-29 17:07:20 |
|  2 | NULL                |
|  3 | NULL                |
|  4 | 2019-01-29 17:07:54 |
|  5 | 2019-01-29 00:00:00 |
|  6 | 2017-08-25 15:30:35 |
|  7 | NULL                |
|  8 | 2016-12-25 16:55:55 |
|  9 | NULL                |
| 10 | 2014-11-12 10:20:23 |
| 11 | 2020-01-01 06:45:23 |
+----+---------------------+
11 rows in set (0.00 sec)

以下是将空值放在末尾且以日期降序排序的查询语句：

mysql> select *from DateColumnWithNullDemo
   -> order by (LoginDateTime IS NULL), LoginDateTime DESC;

以下是输出结果：

+----+---------------------+
| Id | LoginDateTime       |
+----+---------------------+
| 11 | 2020-01-01 06:45:23 |
|  4 | 2019-01-29 17:07:54 |
|  5 | 2019-01-29 00:00:00 |
|  1 | 2018-01-29 17:07:20 |
|  6 | 2017-08-25 15:30:35 |
|  8 | 2016-12-25 16:55:55 |
| 10 | 2014-11-12 10:20:23 |
|  2 | NULL                |
|  3 | NULL                |
|  7 | NULL                |
|  9 | NULL                |
+----+---------------------+
11 rows in set (0.00 sec)

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