Why Doesn't `WHERE x = NULL` Work for Finding NULL Values in SQL?-Mysql Tutorial-php.cn

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Why Doesn't `WHERE x = NULL` Work for Finding NULL Values in SQL?

Mary-Kate Olsen

Jan 21, 2025 pm 01:16 PM

Why Doesn't `WHERE x = NULL` Work for Finding NULL Values in SQL?

SQL's NULL Conundrum: Understanding = NULL vs. IS NULL

Working with NULL values in SQL often presents unexpected behavior. The key to correctly identifying NULLs lies in understanding the difference between WHERE x = NULL and WHERE x IS NULL.

WHERE x IS NULL directly checks if the value of x is explicitly NULL. It's important to note this doesn't include zeros or empty strings, which are distinct values in SQL.

Conversely, WHERE x = NULL attempts to compare x to NULL. This comparison always results in NULL because SQL treats any comparison involving a NULL value as NULL, which evaluates to false in a WHERE clause.

Thus, to effectively locate rows containing NULL values, WHERE x IS NULL is the correct approach. WHERE x = NULL will invariably return an empty result set due to SQL's unique handling of NULL comparisons. Using the proper syntax ensures accurate query results when dealing with NULL data.

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