SQL NULL Handling: How ISNULL, COALESCE, and NULLIF Work

Part 2 of a SQL NULL series covers three key functions for managing missing or invalid data in databases. The ISNULL function replaces NULL values with a specified default, though it is not supported in PostgreSQL, which relies on COALESCE instead. COALESCE is more flexible, accepting multiple fallback values and returning the first non-null result it encounters. NULLIF works in the opposite direction, returning NULL when two compared values are equal, making it useful for normalizing bad data or preventing division-by-zero errors. Together, these functions help developers write more reliable queries when datasets contain missing, unknown, or placeholder values.