如何使用MySQL查询检索NULL的相应值？

可以使用 IS NULL 属性来实现这一点。让我们首先创建一张表 –

mysql> create table DemoTable
(
   EmployeeName varchar(100),
   EmployeeAge int
);
Query OK, 0 rows affected (0.59 sec)

使用插入命令向表中插入一些记录-

mysql> insert into DemoTable values('Chris',32);
Query OK, 1 row affected (0.11 sec)
mysql> insert into DemoTable values('David',45);
Query OK, 1 row affected (0.09 sec)
mysql> insert into DemoTable values('Bob',NULL);
Query OK, 1 row affected (0.16 sec)
mysql> insert into DemoTable values('Sam',28);
Query OK, 1 row affected (0.14 sec)

使用 select 语句从表中显示所有记录 –

mysql> select *from DemoTable;

将会产生以下输出 –

+--------------+-------------+
| EmployeeName | EmployeeAge |
+--------------+-------------+
| Chris        |          32 |
| David        |          45 |
| Bob          |        NULL |
| Sam          |          28 |
+--------------+-------------+
4 rows in set (0.00 sec)

检索NULL的相应值 –

mysql> select *from DemoTable where EmployeeAge IS NULL;

将会产生以下输出 –

+--------------+-------------+
| EmployeeName | EmployeeAge |
+--------------+-------------+
| Bob          | NULL        |
+--------------+-------------+
1 row in set (0.00 sec)

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