由于最近項目，有這樣一個需求，是把數(shù)據(jù)庫中的兩列數(shù)據(jù)互換，經(jīng)過好久才搞定，這里寫個簡單實例，做過記錄。
1.創(chuàng)建表及記錄用于測試
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',
`original_price` decimal(5,2) unsigned NOT NULL COMMENT '原價',
`price` decimal(5,2) unsigned NOT NULL COMMENT '現(xiàn)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(zhí)行的結(jié)果只會使original_price與price的值都是price的值，因為update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 | 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(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 | 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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