mysql - 如何根据 mysql 表中的其他 2 列设置列值？

Question

在 mySql 中，我试图根据同一个表的其他 2 列的值来设置列的值 (total)。

http://sqlfiddle.com/#!9/e9c27a/1

CREATE TABLE IF NOT EXISTS `order_total` (
    `order_total_id` int(10) NOT NULL AUTO_INCREMENT,
    `order_id` int(11) NOT NULL,
    `code` varchar(32) NOT NULL,
    `title` varchar(255) NOT NULL,
    `value` decimal(15,4) NOT NULL DEFAULT '0.0000',
    `sort_order` int(3) NOT NULL,
    PRIMARY KEY (`order_total_id`),
    KEY `order_id` (`order_id`)
) ENGINE=MyISAM AUTO_INCREMENT=244 DEFAULT CHARSET=utf8;

INSERT INTO `order_total` (`order_total_id`, `order_id`, `code`, `title`, `value`, `sort_order`) VALUES
(241, 80, 'sub_total', 'Sub-Total', '400.0000', 1),
(242, 80, 'shipping', 'Free Shipping', '10.0000', 3),
(243, 80, 'total', 'Total', '0', 9);

我尝试了这样一个在本地 mySql 中工作的代码，但我想也许有更好的方法来做到这一点。

UPDATE order_total ot 
INNER JOIN (
    SELECT order_id, value
    FROM order_total
        WHERE code = 'sub_total'
    GROUP BY order_id
) o ON ot.order_id = o.order_id
INNER JOIN (
    SELECT order_id, value
    FROM order_total
        WHERE code = 'shipping'
    GROUP BY order_id
) o2 ON ot.order_id = o2.order_id
SET ot.value = o.value + o2.value 
WHERE ot.code = 'total' AND ot.order_id = 80

如何做更有效率？

Answer 1

您可以使用一个查询来计算总数，如下所示:

update order_total ot 
INNER JOIN (
   SELECT order_id, sum(value) value
   FROM order_total
   WHERE code = 'sub_total' or code= 'shipping'
   GROUP BY order_id
) o ON ot.order_id = o.order_id
SET ot.value = o.value
WHERE ot.code = 'total' AND ot.order_id = 80;