This article explains why MySQL discourages using NULL as a default column value, demonstrates how NULL affects indexing, comparisons, and aggregate functions, and shows through concrete examples that improper NULL handling can lead to unexpected query results and performance degradation.
This article explores how MySQL decides whether queries with IS NULL or IS NOT NULL predicates can use an index, presenting three concrete examples with varying data sizes and NULL distributions, and explains the underlying storage of NULL values and optimizer cost decisions.
This article explains how the PHP is_null function can be used to determine whether a variable holds a null value, demonstrates its behavior with example code, and discusses the practical implications for conditional logic in backend development.
This article explains how the PHP built‑in function is_null can be used to determine whether a variable holds a null value, demonstrates its behavior with example code, and describes the resulting true or false outcomes for different variable types.
This article explains the special nature of NULL in SQL, how to correctly test for NULL using IS NULL, the three‑valued logic of true/false/unknown, and the pitfalls of NOT, NOT IN, and Oracle’s handling of empty strings versus NULL.
This article explains the special nature of NULL in relational databases, demonstrates the correct use of IS NULL versus = NULL, explores three-valued logic, and clarifies how NULL interacts with NOT, NOT IN, and empty strings across different database systems.
This article explains the meaning of NULL in SQL, distinguishes the two conceptual types of unknown and not‑applicable, describes three‑valued logic, shows why IS NULL must be used instead of = NULL, and warns about pitfalls such as NOT IN with NULL and improper CASE expressions.
