大家好，我是考100分的小小码 ，祝大家学习进步，加薪顺利呀。今天说一说mysql互换表中两列数据方法「建议收藏」,希望您对编程的造诣更进一步.
1.创建表及记录用于测试
CREATE TABLE
product(
idint(10) unsigned NOT NULL AUTO_INCREMENT COMMENT “产品id”,
namevarchar(50) NOT NULL COMMENT “产品名称”,
original_pricedecimal(5,2) unsigned NOT NULL COMMENT “原价”,
pricedecimal(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)代码100分
2.互换original_price与price的值
新手可能会使用以下方法进行互换
代码100分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：
代码100分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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