Mysql 之 条件判断、循环语句
官方英文文档：
http://dev.mysql.com/doc/refman/5.0/en/flow-control-statements.html

**************************    IF    **************************
语法：

IF search_condition THEN statement_list
    [ELSEIF search_condition THEN statement_list] ...
    [ELSE statement_list]
END IF

实例：

DELIMITER$$

DROP PROCEDURE IF EXISTS pro_if$$
CREATE PROCEDURE pro_if(
	i INT
)
BEGIN
	IF i < 60 THEN
		SELECT '需继续努力，争取过线！' AS result;
	ELSEIF i < 85 THEN
		SELECT '再努力点，争取达优！' AS result;
	ELSE 
		SELECT '不错哦，恭喜，恭喜！' AS result;
	END IF;
END$$

**************************    CASE    **************************
语法：

CASE case_value
    WHEN when_value THEN statement_list
    [WHEN when_value THEN statement_list] ...
    [ELSE statement_list]
END CASE

Or:

CASE
    WHEN search_condition THEN statement_list
    [WHEN search_condition THEN statement_list] ...
    [ELSE statement_list]
END CASE

实例：

DELIMITER$$

DROP PROCEDURE IF EXISTS pro_case$$
CREATE PROCEDURE pro_case(
	i INT
)
BEGIN
	CASE i
	WHEN 1 THEN SELECT 'you male!' AS result;
	WHEN 0 THEN SELECT 'you female!' AS result;
	ELSE
		SELECT 'third sex!' AS result;
	END CASE;
END$$