IF..THEN 语句中的 mysql 过程错误答案

【问题标题】：mysql procedure error in IF..THEN statementIF..THEN 语句中的 mysql 过程错误
【发布时间】：2016-06-09 13:39:31
【问题描述】：

所以我有这个程序来计算运费。我需要从匹配行中选择两个值。并且根据基于in_quantity的条件，在这两个先前选择的值中，一个将设置为out_total。

DELIMITER $$
CREATE PROCEDURE freight_calc(
    IN in_delivery_location VARCHAR(100),
    IN in_category_id INT(11),
    IN in_quantity INT(11),   
    OUT out_total DECIMAL(10,2)
    )
BEGIN
    DECLARE val1 DECIMAL(10,2);
    DECLARE val2 DECIMAL(10,2);

    SELECT col1,col2 INTO val1, val2 
    FROM `freight_rules` fr
    WHERE fr.category_id = in_category_id AND fr.delivery_location = in_delivery_location;

    IF(in_quantity <= 9) THEN
        out_total = val1;
    END IF;

    IF(in_quantity > 9) THEN
        out_total = val2;
    END IF;

END$$
DELIMITER ;

执行时会出现以下错误 -

#1064 - You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near '= val1;
    END IF;

    IF(in_quantity > 9) THEN
        out_total = val2' at line 16

【问题讨论】：

标签： mysql stored-procedures mysql-routines

【解决方案1】：

因为任何值都分配给 mysql 中的变量，所以我们使用 SET 关键字。所以只在过程中改变

SET out_total = val1;
SET out_total = val1;

DELIMITER $$
CREATE PROCEDURE freight_calc(
    IN in_delivery_location VARCHAR(100),
    IN in_category_id INT(11),
    IN in_quantity INT(11),   
    OUT out_total DECIMAL(10,2)
    )
BEGIN
    DECLARE val1 DECIMAL(10,2);
    DECLARE val2 DECIMAL(10,2);

    SELECT col1,col2 INTO val1, val2 
    FROM `freight_rules` fr
    WHERE fr.category_id = in_category_id AND fr.delivery_location = in_delivery_location;

    IF(in_quantity <= 9) THEN
      SET out_total = val1;
    END IF;

    IF(in_quantity > 9) THEN
       SET out_total = val1;
    END IF;

END$$
DELIMITER ;

【讨论】：