How to Handle NULL Values in MySQL

NULL means 'unknown', and it behaves unlike any value: it isn't equal to anything, not even itself. Mishandled NULLs silently distort counts, averages, and joins — so every analyst needs these patterns.

Key Points

• Test with IS NULL / IS NOT NULL — never col = NULL
• Replace for display: COALESCE(phone, 'Not provided') or IFNULL(x, 0)
• COUNT(col) skips NULLs; COUNT(*) doesn't — pick deliberately
• AVG ignores NULLs; decide whether that's what your metric intends
• NULLs in join keys never match — rows silently disappear
• NULLIF(a, b) returns NULL when a=b, handy for avoiding divide-by-zero