**Performance:**

- IS NULL can use indexes

- IS NOT NULL can use indexes

- COALESCE may prevent index usage

- Consider NOT NULL constraints for critical columns

IS NULL and IS NOT NULL can use indexes

COALESCE may prevent index usage

Consider NOT NULL constraints for performance

Filter NULL early in query execution

Using = NULL instead of IS NULL

Using != NULL instead of IS NOT NULL

NOT IN with NULL returns no rows

Forgetting NULL in OR conditions

Assuming NULL = NULL is true