由于最近项目,有这样一个需求,是把数据库中的两列数据互换,经过好久才搞定,这里写个简单实例,做过记录。
1.创建表及记录用于测试
CREATE TABLE `product` ( `id` int(10) unsigned NOT NULL AUTO_INCREMENT COMMENT '产品id',`name` varchar(50) NOT NULL COMMENT '产品名称',`original_price` decimal(5,2) unsigned NOT NULL COMMENT '原价',`price` decimal(5,2) unsigned NOT NULL COMMENT '现价',PRIMARY KEY (`id`) ) ENGINE=InnoDB DEFAULT CHARSET=utf8; INSERT INTO `product` (`id`,`name`,`original_price`,`price`) VALUES (NULL,'雪糕','5','3.5'),(NULL,'鲜花','18','15'),'甜点','25','12.5'),'玩具','55','45'),'钱包','285','195');
mysql> select * from product; +----+--------+----------------+--------+ | id | name | original_price | price | +----+--------+----------------+--------+ | 1 | 雪糕 | 5.00 | 3.50 | | 2 | 鲜花 | 18.00 | 15.00 | | 3 | 甜点 | 25.00 | 12.50 | | 4 | 玩具 | 55.00 | 45.00 | | 5 | 钱包 | 285.00 | 195.00 | +----+--------+----------------+--------+ 5 rows in set (0.00 sec)
2.互换original_price与price的值
新手可能会使用以下方法进行互换
update product set original_price=price,price=original_price;
但这样执行的结果只会使original_price与price的值都是price的值,因为update有顺序的,
先执行original_price=price ,original_price的值已经更新为price,
然后执行price=original_price,这里相当于没有更新。
执行结果:
mysql> select * from product; +----+--------+----------------+--------+ | id | name | original_price | price | +----+--------+----------------+--------+ | 1 | 雪糕 | 5.00 | 3.50 | | 2 | 鲜花 | 18.00 | 15.00 | | 3 | 甜点 | 25.00 | 12.50 | | 4 | 玩具 | 55.00 | 45.00 | | 5 | 钱包 | 285.00 | 195.00 | +----+--------+----------------+--------+ 5 rows in set (0.00 sec) mysql> update product set original_price=price,price=original_price; Query OK,5 rows affected (0.00 sec) Rows matched: 5 Changed: 5 Warnings: 0 mysql> select * from product; +----+--------+----------------+--------+ | id | name | original_price | price | +----+--------+----------------+--------+ | 1 | 雪糕 | 3.50 | 3.50 | | 2 | 鲜花 | 15.00 | 15.00 | | 3 | 甜点 | 12.50 | 12.50 | | 4 | 玩具 | 45.00 | 45.00 | | 5 | 钱包 | 195.00 | 195.00 | +----+--------+----------------+--------+ 5 rows in set (0.00 sec)
正确的互换方法如下:
update product as a,product as b set a.original_price=b.price,a.price=b.original_price where a.id=b.id;
执行结果:
mysql> select * from product;
+----+--------+----------------+--------+
| id | name | original_price | price |
+----+--------+----------------+--------+
| 1 | 雪糕 | 5.00 | 3.50 |
| 2 | 鲜花 | 18.00 | 15.00 |
| 3 | 甜点 | 25.00 | 12.50 |
| 4 | 玩具 | 55.00 | 45.00 |
| 5 | 钱包 | 285.00 | 195.00 |
+----+--------+----------------+--------+
5 rows in set (0.00 sec)
mysql> update product as a,a.price=b.original_price where a.id=b.id;
Query OK,5 rows affected (0.01 sec)
Rows matched: 5 Changed: 5 Warnings: 0
mysql> select * from product;
+----+--------+----------------+--------+
| id | name | original_price | price |
+----+--------+----------------+--------+
| 1 | 雪糕 | 3.50 | 5.00 |
| 2 | 鲜花 | 15.00 | 18.00 |
| 3 | 甜点 | 12.50 | 25.00 |
| 4 | 玩具 | 45.00 | 55.00 |
| 5 | 钱包 | 195.00 | 285.00 |
+----+--------+----------------+--------+
5 rows in set (0.00 sec)
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