MySQL流程控制语句

/**清除原先的函数**/
DROP FUNCTION IF EXISTS `fun_test`;

/**创建函数**/
CREATE FUNCTION `fun_test`
/**设置函数参数**/
(a DOUBLE,b DOUBLE)
/**设置返回值类型**/
RETURNS VARCHAR(500)

BEGIN
/**设置成员变量**/
DECLARE res VARCHAR(500);
SET res = '';

/** If...else...语句 **/
IF a>0 THEN SET res = CONCAT(res,'a > 0; ');
ELSEIF a<0 THEN SET res = CONCAT(res,'a < 0; ');
ELSE SET res = CONCAT(res,'a = 0; ');
END IF;

/** case...when...语句 类似于switch **/
CASE b 
WHEN 0 THEN SET res = CONCAT(res,'b == 0; ');
ELSE SET res = CONCAT(res,'b != 0; ');
END CASE;

/** loop语句 类似于for循环，使用LEAVE跳出循环 **/
SET @count=0; 
loop_eg: LOOP
SET @count=@count+1;
IF @count<2 THEN SET  res = CONCAT(res,'LOOP循环测试:');
ELSE LEAVE loop_eg; 
END IF;
END LOOP loop_eg; 

/** loop语句 类似于for循环，使用ITERATE跳出本次循环 **/
SET @count=0; 
loop_eg: LOOP
SET @count=@count+1;
IF @count=1 THEN SET  res = CONCAT(res,'1');
ELSEIF @count=2 THEN ITERATE loop_eg; SET  res = CONCAT(res,'2');
ELSEIF @count=3 THEN SET res = CONCAT(res,'3;');
ELSE LEAVE loop_eg; 
END IF;
END LOOP loop_eg; 

/** repeat...util...语句 类似于do...WHILE...语句 **/
SET @count=0; 
REPEAT 
SET @count=@count+1;
SET  res = CONCAT(res,@count);
UNTIL @count=5 
END REPEAT ;

/** while...语句 **/
WHILE @count<10 DO 
SET @count=@count+1; 
SET  res = CONCAT(res,@count);
END WHILE ; 

RETURN res;
END;

/**测试函数**/
SELECT fun_test(1,2)