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mysql 實(shí)現(xiàn)互換表中兩列數(shù)據(jù)方法簡(jiǎn)單實(shí)例

更新時(shí)間：2016年10月21日 10:26:50 投稿：lqh

這篇文章主要介紹了mysql 實(shí)現(xiàn)互換表中兩列數(shù)據(jù)方法簡(jiǎn)單實(shí)例的相關(guān)資料,需要的朋友可以參考下

由于最近項(xiàng)目，有這樣一個(gè)需求，是把數(shù)據(jù)庫(kù)中的兩列數(shù)據(jù)互換，經(jīng)過(guò)好久才搞定，這里寫(xiě)個(gè)簡(jiǎn)單實(shí)例，做過(guò)記錄。

1.創(chuàng)建表及記錄用于測(cè)試

CREATE TABLE `product` (
 `id` int(10) unsigned NOT NULL AUTO_INCREMENT COMMENT '產(chǎn)品id',
 `name` varchar(50) NOT NULL COMMENT '產(chǎn)品名稱(chēng)',
 `original_price` decimal(5,2) unsigned NOT NULL COMMENT '原價(jià)',
 `price` decimal(5,2) unsigned NOT NULL COMMENT '現(xiàn)價(jià)',
 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(diǎn)', '25', '12.5'), 
(NULL, '玩具', '55', '45'), 
(NULL, '錢(qián)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(diǎn)  |     25.00 | 12.50 |
| 4 | 玩具  |     55.00 | 45.00 |
| 5 | 錢(qián)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(huì)使用以下方法進(jìn)行互換

update product set original_price=price,price=original_price;

但這樣執(zhí)行的結(jié)果只會(huì)使original_price與price的值都是price的值，因?yàn)閡pdate有順序的，

先執(zhí)行original_price=price , original_price的值已經(jīng)更新為price，

然后執(zhí)行price=original_price，這里相當(dāng)于沒(méi)有更新。

執(zhí)行結(jié)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(diǎn)  |     25.00 | 12.50 |
| 4 | 玩具  |     55.00 | 45.00 |
| 5 | 錢(qián)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(diǎn)  |     12.50 | 12.50 |
| 4 | 玩具  |     45.00 | 45.00 |
| 5 | 錢(qián)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(zhí)行結(jié)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(diǎn)   |          25.00 | 12.50 |
| 4 | 玩具   |          55.00 | 45.00 |
| 5 | 錢(qián)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(diǎn)   |          12.50 | 25.00 |
| 4 | 玩具   |          45.00 | 55.00 |
| 5 | 錢(qián)包   |         195.00 | 285.00 |
+----+--------+----------------+--------+
5 rows in set (0.00 sec)

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