ISNULL vs. COALESCE for Null Checks: Which Performs Better?

Debating ISNULL vs. COALESCE for Condition Checking

Consider the scenario where you need to validate a single expression for existence. Should you utilize a default value or adopt ISNULL as a superior practice? Furthermore, does their performance differ significantly?

Understanding COALESCE and ISNULL

COALESCE evaluates multiple parameters, returning the first non-null value. ISNULL, on the other hand, explicitly checks for a null value, returning the default provided or a specified replacement value.

Performance Considerations

A Microsoft Connect report outlines the performance nuances between COALESCE and ISNULL. It reveals that COALESCE is translated into a CASE expression, potentially leading to duplicate subquery execution if the subquery evaluates to null. This can impact performance in complex queries.

Recommended Approach

Based on the aforementioned report, ISNULL is preferable to COALESCE for checking a single expression's existence. It avoids unnecessary subquery duplication and potentially improves performance.

The above is the detailed content of ISNULL vs. COALESCE for Null Checks: Which Performs Better?. For more information, please follow other related articles on the PHP Chinese website!