Usage of is null in sql

IS NULL is an operator in SQL that checks whether a field or expression is a NULL value. The syntax is "Field IS NULL" or "Expression IS NULL". It is commonly used to check whether a field is NULL, compare NULL values ​​to other values, or exclude rows with NULL values ​​from the result set.

Usage of IS NULL in SQL

What is IS NULL?

IS NULL is a SQL operator that checks whether a field or expression is a NULL value. A NULL value means there is no value in the field or the value is unknown.

Syntax

Field IS NULL
Expression IS NULL

## When to use IS NULL?

The IS NULL operator is typically used in the following situations:

Check whether a field is NULL to determine whether certain conditions are true.
• Compare NULL values ​​with other values.
• Exclude rows with NULL values ​​from the result set.

Example

Check if a field is NULL:

SELECT * FROM table_name WHERE field_name IS NULL;

This query will return

table_name All rows in the table where field_name is NULL.

Compare NULL values ​​with other values:

SELECT * FROM table_name WHERE field_name = 'John' OR field_name IS NULL;

This query will return all

field_name in the table_name table that are 'John' or NULL rows.

Exclude rows with NULL values ​​from the result set:

SELECT * FROM table_name WHERE field_name IS NOT NULL;

This query will return all

field_name in the table_name table Rows that are not NULL.

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