MySQL查询按NULL值排序
让我们首先创建一个表-
mysql> create table DemoTable707 ( StudentId int NOT NULL AUTO_INCREMENT PRIMARY KEY, StudentFirstName varchar(100), StudentMarks int );
使用插入命令在表中插入一些记录-
mysql> insert into DemoTable707(StudentFirstName,StudentMarks) values('John',45);
mysql> insert into DemoTable707(StudentFirstName,StudentMarks) values(NULL,65);
mysql> insert into DemoTable707(StudentFirstName,StudentMarks) values('Chris',78);
mysql> insert into DemoTable707(StudentFirstName,StudentMarks) values(NULL,89);
mysql> insert into DemoTable707(StudentFirstName,StudentMarks) values('Robert',99);
mysql> insert into DemoTable707(StudentFirstName,StudentMarks) values(NULL,34);
mysql> insert into DemoTable707(StudentFirstName,StudentMarks) values('Mike',43);使用select语句显示表中的所有记录-
mysql> select *from DemoTable707;
这将产生以下输出-
+-----------+------------------+--------------+ | StudentId | StudentFirstName | StudentMarks | +-----------+------------------+--------------+ | 1 | John | 45 | | 2 | NULL | 65 | | 3 | Chris | 78 | | 4 | NULL | 89 | | 5 | Robert | 99 | | 6 | NULL | 34 | | 7 | Mike | 43 | +-----------+------------------+--------------+ 7 rows in set (0.00 sec)
以下是按NULL值排序的查询-
mysql> select *from DemoTable707 order by StudentFirstName IS NULL, StudentFirstName DESC;
这将产生以下输出-
+-----------+------------------+--------------+ | StudentId | StudentFirstName | StudentMarks | +-----------+------------------+--------------+ | 5 | Robert | 99 | | 7 | Mike | 43 | | 1 | John | 45 | | 3 | Chris | 78 | | 2 | NULL | 65 | | 4 | NULL | 89 | | 6 | NULL | 34 | +-----------+------------------+--------------+ 7 rows in set (0.00 sec)
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