IS NULL condition in SQL Server

In SQL Server (Transact-SQL), the condition IS NULL is used to check the NULL value. A NULL value in a table is a value in an empty field, in other words, a field with no value.

Syntax condition IS NULL

 IS NULL 'expression' 

Variable name or variable value

expression

Values ​​to check if the value is NULL.

Note

• If the expression has NULL value, the condition returns TRUE result
• If the expression has no NULL value, the condition returns FALSE

For example - SELECT command

Let's look at the example condition NULL in the SELECT statement below.

 SELECT * 
 FROM nhanvien 
 WHERE ho IS NULL; 

This example will return all records in the table if the employee's last name is left blank - or called NULL.

Example - INSERT command

 INSERT INTO nhanvien 
 ((nhanvien_id, ho, ten) 
 SELECT nhanvien_id, ho, ten 
 FROM danhba 
 WHERE ten IS NULL; 

This command will fill in records from the list into the user table in the fields whose employee name is left blank.

Example - UPDATE command

 UPDATE nhanvien 
 SET ten = 'Unknown' 
 WHERE ten IS NULL; 

In this example, the records in the user table whose blank name value will be updated.

Example - DELETE command

 DELETE FROM nhanvien 
 WHERE ho IS NULL; 

This command will delete all records in the table if the value in the last name field is NULL.

Previous article: IN conditions in SQL Server

Next lesson: IS NOT NULL condition in SQL Server