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法律研究MySQL 查询按 NULL 值排序
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 ); Query OK, 0 rows affected (0.59 sec)
使用 insert 命令在表中插入一些记录 -
mysql> insert into DemoTable707(StudentFirstName,StudentMarks) values('John',45);
Query OK, 1 row affected (0.16 sec)
mysql> insert into DemoTable707(StudentFirstName,StudentMarks) values(NULL,65);
Query OK, 1 row affected (0.15 sec)
mysql> insert into DemoTable707(StudentFirstName,StudentMarks) values('Chris',78);
Query OK, 1 row affected (0.19 sec)
mysql> insert into DemoTable707(StudentFirstName,StudentMarks) values(NULL,89);
Query OK, 1 row affected (0.19 sec)
mysql> insert into DemoTable707(StudentFirstName,StudentMarks) values('Robert',99);
Query OK, 1 row affected (0.18 sec)
mysql> insert into DemoTable707(StudentFirstName,StudentMarks) values(NULL,34);
Query OK, 1 row affected (0.13 sec)
mysql> insert into DemoTable707(StudentFirstName,StudentMarks) values('Mike',43);
Query OK, 1 row affected (0.20 sec)使用 select 语句从表中显示所有记录 -
mysql> select *from DemoTable707;
这会产生以下输出 -
+-----------+------------------+--------------+ | 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;
这会产生以下输出 -
+-----------+------------------+--------------+ | 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)
更新于: 2019 年 8 月 21 日
162 次浏览
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