mysql> select IFNULL(1,0);
    -> 1
mysql> select IFNULL(0,10);
    -> 0
mysql> select IFNULL(1/0,10);
    -> 10
mysql> select IFNULL(1/0,'yes');
    -> 'yes'
 
IF(expr1,expr2,expr3) 

mysql> select IF(1>2,2,3);
    -> 3
mysql> select IF(1<2,'yes','no');
    -> 'yes'
mysql> select IF(strcmp('test','test1'),'yes','no');
    -> 'no'

mysql> select IF(0.1,1,0);
    -> 0
mysql> select IF(0.1<>0,1,0);
    -> 1

CASE value WHEN [compare-value] THEN result [WHEN [compare-value] THEN result ...] [ELSE result] END 
　 
CASE WHEN [condition] THEN result [WHEN [condition] THEN result ...] [ELSE result] END 

mysql> SELECT CASE 1 WHEN 1 THEN "one" WHEN 2 THEN "two" ELSE "more" END;
    -> "one"
mysql> SELECT CASE WHEN 1>0 THEN "true" ELSE "false" END;
    -> "true"
mysql> SELECT CASE BINARY "B" when "a" then 1 when "b" then 2 END;
-> NULL