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What do COALESCE and NULLIF do?

Q: What do COALESCE and NULLIF do?

**COALESCE(a, b, c)** returns the first non-NULL argument — great for defaults. **NULLIF(a, b)** returns NULL if `a = b` (else `a`) — handy to avoid divide-by-zero by turning a 0 divisor into NULL.

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COALESCE(a, b, c) returns the first non-NULL argument — great for defaults. NULLIF(a, b) returns NULL if a = b (else a) — handy to avoid divide-by-zero by turning a 0 divisor into NULL.

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