SELECT AVG(bonus) FROM employees;

-- Expecting this to treat NULL as $0

SELECT AVG(COALESCE(bonus, 0)) FROM employees;

-- Explicitly treats NULL as $0

AVG(bonus) calculates average of only non-NULL bonuses. Use COALESCE to explicitly treat NULL as zero.

Use COALESCE(column, 0) if you want to treat NULL as zero in AVG or SUM

High

AVG ignores NULL values - does not treat them as zero

SELECT SUM(bonus) FROM employees;

-- Expecting 0 when all bonuses are NULL

SELECT COALESCE(SUM(bonus), 0) FROM employees;

-- Returns 0 when all bonuses are NULL

If all bonus values are NULL, SUM(bonus) returns NULL. Use COALESCE for NULL-safe arithmetic.

Wrap aggregates in COALESCE when you need NULL-safe results

High

SUM of all NULL values returns NULL, not 0