syntax：
IF(expr,if_true_expr,if_false_expr)
syntax：
CASE value
WHEN compare_value_1 THEN result_1
WHEN compare_value_2 THEN result_2
…
ELSE result END
second form：
CASE
WHEN condition_1 THEN result_1
WHEN condition_2 THEN result_2
…
ELSE result END
CASE statement (for Stored Procedure)
syntax:
CASE case_expression
WHEN when_expression_1 THEN commands
WHEN when_expression_2 THEN commands
...
ELSE commands
END CASE;