What is NULL in MySQL? Is NULL the same as 0 or an empty string?

NULL means “no value” or “unknown”. It is not zero and not an empty string.

SELECT NULL = NULL, NULL IS NULL, 0 IS NULL, '' IS NULL;

NULL = NULL gives NULL (not true). Always use IS NULL and IS NOT NULL. Aggregate functions ignore NULL, and COALESCE(column, 0) replaces NULL with a value.

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