NULLIF (exp1, exp2)
- NULL if exp1 and exp2 are equal, otherwise exp1
- CASE WHEN expr1 = expr2 THEN NULL ELSE expr1 END
- If the numerator is zero in division, an error occurs. Use of NULLIF is convenient. num1 / NULLIF (num2, 0): If num2 is 0, the denominator becomes NULL and no error occurs. The result of division is NULL.