Usage of isnull function in sql

The ISNULL() function in SQL is used to check whether an expression is NULL and return the specified value. Usage is as follows: checks for a NULL value and returns a replacement value. Prevent divide-by-zero errors. Merge two fields to avoid duplication.

Usage of the ISNULL() function in SQL

The ISNULL() function is used to check whether the expression is NULL , and returns the specified value. The syntax is as follows:

ISNULL(expression, default_value)

Where:

• expression: The expression to be checked.
• default_value: The value returned if expression is NULL.

Usage example:

• Return the alternative value of NULL value:

SELECT ISNULL(name, 'Unknown') FROM table_name;

• Prevent division by zero errors:

UPDATE table_name SET value = value / ISNULL(divisor, 1);

• Merge two fields to avoid duplication:

SELECT ISNULL(field1, field2) AS combined_field FROM table_name;

Note:

• default_value can be any data type, but it must be compatible with the data type of expression.
• If expression is not NULL, the ISNULL() function returns expression itself.
• The ISNULL() function is similar to the COALESCE() function, but the COALESCE() function can accept multiple default_values, while the ISNULL() function can only accept one.

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