MySQL 查询两个字段和 NULL 值按时间顺序排列

让我们首先创建一个表-

mysql> create table DemoTable -> ( -> FirstName varchar(100), -> LastName varchar(100) -> ); Query OK, 0 rows affected (1.39 sec)

使用插入命令在表中插入一些记录-

mysql> insert into DemoTable values(Sam,Brown); Query OK, 1 row affected (0.25 sec) mysql> insert into DemoTable values(null,Smith); Query OK, 1 row affected (0.16 sec) mysql> insert into DemoTable values(David,Taylor); Query OK, 1 row affected (0.22 sec) mysql> insert into DemoTable values(Mike,null); Query OK, 1 row affected (0.45 sec)

使用select语句显示表中的所有记录-

mysql> select *from DemoTable;

输出结果

这将产生以下输出-

+-----------+----------+ | FirstName | LastName | +-----------+----------+ | Sam | Brown | | NULL | Smith | | David | Taylor | | Mike | NULL | +-----------+----------+ 4 rows in set (0.06 sec)

这是按两个字段排序的查询，按时间顺序可能为NULL值-

mysql> select *from DemoTable order by coalesce(FirstName,LastName);

输出结果

这将产生以下输出-

+-----------+----------+ | FirstName | LastName | +-----------+----------+ | David | Taylor | | Mike | NULL | | Sam | Brown | | NULL | Smith | +-----------+----------+ 4 rows in set (0.04 sec)