Why 'WHERE x = NULL' Always Fails in SQL and How to Fix It

In SQL, using 'WHERE column = NULL' to find missing values is a common mistake that silently returns zero rows, even when NULL values are clearly present in the table. This happens because SQL treats NULL as 'unknown' rather than 'nothing', and any comparison with NULL yields UNKNOWN — not TRUE or FALSE — causing all rows to be filtered out. The correct approach is to use the dedicated 'IS NULL' or 'IS NOT NULL' operators, which are specifically designed to test for the absence of a value. Similarly, 'WHERE column != NULL' does not return rows with actual values; only 'IS NOT NULL' does that correctly. Developers can quickly detect such issues by running an unfiltered 'SELECT *' first to spot NULL values before applying any WHERE clause logic.