mysql 实现互换表中两列数据方法简单实例

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'), 
(NULL, '甜点', '25', '12.5'), 
(NULL, '玩具', '55', '45'), 
(NULL, '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, product as b set a.original_price=b.price, 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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