mysql的存储过程中的语句ifcase循环语句

IF expression THEN 
   statements;
END IF;

参数：p_customerlevel用来存储客户的级别，并由调用程序使用。

DELIMITER $$

CREATE PROCEDURE GetCustomerLevel(
    in  p_customerNumber int(11), 
    out p_customerLevel  varchar(10))

BEGIN
    DECLARE creditlim double;

    SELECT creditlimit INTO creditlim
    FROM customers
    WHERE customerNumber = p_customerNumber;

    IF creditlim > 50000 THEN
        SET p_customerLevel = 'PLATINUM';
    ELSEIF (creditlim <= 50000 AND creditlim >= 10000) THEN
        SET p_customerLevel = 'GOLD';
    ELSEIF creditlim < 10000 THEN
        SET p_customerLevel = 'SILVER';
    END IF;
END$$

CASE  case_expression
   WHEN when_expression_1 THEN commands
   WHEN when_expression_2 THEN commands
   ...
   ELSE commands
END CASE;
SQL

您可以使用简单CASE语句来检查表达式的值与一组唯一值的匹配。

case_expression可以是任何有效的表达式。我们将case_expression的值与每个WHEN子句中的when_expression进行比较，例如when_expression_1，when_expression_2等。如果case_expression和when_expression_n的值相等，则执行相应的WHEN分支中的命令(commands)。如果都不匹配，就执行ELSE commands语句。

DELIMITER $$

CREATE PROCEDURE GetCustomerShipping(
 in  p_customerNumber int(11), 
 out p_shiping        varchar(50))
BEGIN
    DECLARE customerCountry varchar(50);

    SELECT country INTO customerCountry
 FROM customers
 WHERE customerNumber = p_customerNumber;

    CASE customerCountry
 WHEN  'USA' THEN
    SET p_shiping = '2-day Shipping';
 WHEN 'Canada' THEN
    SET p_shiping = '3-day Shipping';
 ELSE
    SET p_shiping = '5-day Shipping';
 END CASE;

END$$

WHILE循环

WHILE语句的语法如下：

WHILE expression DO
   statements
END WHILE

DELIMITER $$
 DROP PROCEDURE IF EXISTS test_mysql_while_loop$$
 CREATE PROCEDURE test_mysql_while_loop()
 BEGIN
 DECLARE x  INT;
 DECLARE str  VARCHAR(255);

 SET x = 1;
 SET str =  '';

 WHILE x  <= 5 DO
 SET  str = CONCAT(str,x,',');
 SET  x = x + 1; 
 END WHILE;

 SELECT str;
 END$$
DELIMITER ;

REPEAT循环

REPEAT循环语句的语法如下：

REPEAT
 statements;
UNTIL expression
END REPEAT

• LEAVE语句用于立即退出循环，而无需等待检查条件。LEAVE语句的工作原理就类似PHP，C/C++，Java等其他语言的break语句一样。
• ITERATE语句允许您跳过剩下的整个代码并开始新的迭代。ITERATE语句类似于PHP，C/C++，Java等中的continue语句。