mysql 實現互換表中兩列數據方法簡單實例

由於最近項目，有這樣一個需求，是把數據庫中的兩列數據互換，經過好久才搞定，這裡寫個簡單實例，做過記錄。

1.創建表及記錄用於測試

CREATE TABLE `product` (
 `id` int(10) unsigned NOT NULL AUTO_INCREMENT COMMENT '產品id',
 `name` varchar(50) NOT NULL COMMENT '產品名稱',
 `original_price` decimal(5,2) unsigned NOT NULL COMMENT '原價',
 `price` decimal(5,2) unsigned NOT NULL COMMENT '現價',
 PRIMARY KEY (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;

INSERT INTO `product` (`id`, `name`, `original_price`, `price`) VALUES 
(NULL, '雪糕', '5', '3.5'), 
(NULL, '鮮花', '18', '15'), 
(NULL, '甜點', '25', '12.5'), 
(NULL, '玩具', '55', '45'), 
(NULL, '錢包', '285', '195');

mysql> select * from product;
+----+--------+----------------+--------+
| id | name  | original_price | price |
+----+--------+----------------+--------+
| 1 | 雪糕  |      5.00 |  3.50 |
| 2 | 鮮花  |     18.00 | 15.00 |
| 3 | 甜點  |     25.00 | 12.50 |
| 4 | 玩具  |     55.00 | 45.00 |
| 5 | 錢包  |     285.00 | 195.00 |
+----+--------+----------------+--------+
5 rows in set (0.00 sec)

2.互換original_price與price的值

新手可能會使用以下方法進行互換

update product set original_price=price,price=original_price;

但這樣執行的結果只會使original_price與price的值都是price的值，因為update有順序的，

先執行original_price=price , original_price的值已經更新為price，

然後執行price=original_price，這裡相當於沒有更新。

執行結果：

mysql> select * from product;
+----+--------+----------------+--------+
| id | name  | original_price | price |
+----+--------+----------------+--------+
| 1 | 雪糕  |      5.00 |  3.50 |
| 2 | 鮮花  |     18.00 | 15.00 |
| 3 | 甜點  |     25.00 | 12.50 |
| 4 | 玩具  |     55.00 | 45.00 |
| 5 | 錢包  |     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 | 鮮花  |     15.00 | 15.00 |
| 3 | 甜點  |     12.50 | 12.50 |
| 4 | 玩具  |     45.00 | 45.00 |
| 5 | 錢包  |     195.00 | 195.00 |
+----+--------+----------------+--------+
5 rows in set (0.00 sec)

正確的互換方法如下：

update product as a, product as b set a.original_price=b.price, a.price=b.original_price where a.id=b.id;

執行結果：

mysql> select * from product;
+----+--------+----------------+--------+
| id | name   | original_price | price  |
+----+--------+----------------+--------+
|  1 | 雪糕   |           5.00 |   3.50 |
|  2 | 鮮花   |          18.00 |  15.00 |
|  3 | 甜點   |          25.00 |  12.50 |
|  4 | 玩具   |          55.00 |  45.00 |
|  5 | 錢包   |         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 | 鮮花   |          15.00 |  18.00 |
|  3 | 甜點   |          12.50 |  25.00 |
|  4 | 玩具   |          45.00 |  55.00 |
|  5 | 錢包   |         195.00 | 285.00 |
+----+--------+----------------+--------+
5 rows in set (0.00 sec)

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