How to retrieve the corresponding value for NULL with a MySQL query?

For this, use IS NULL property. Let us first create a table −

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

Insert some records in the table using insert command −

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)

Display all records from the table using select statement −

mysql> select *from DemoTable;

This will produce the following output −

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

Retrieve the corresponding value for NULL −

mysql> select *from DemoTable where EmployeeAge IS NULL;

This will produce the following output −

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