Overview of Control Flow Functions

Name	Description
CASE	CASE WHEN statement is used to calculate a list of conditions and return one of multiple possible result expressions
IF()	IF(expr1,expr2,expr3), when expr1 is TRUE, it returns expr2; otherwise, it returns expr3
IFNULL()	IFNULL(expr1,expr2), when expr1 is not NULL, it returns expr1; otherwise it returns expr2
NULLIF()	NULLIF(expr1,expr2), when expr1 = expr2, returns NULL; otherwise, returns the value of expr1