对于mysql互换表中2列数据方法的讲解1

[摘要]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_...

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: 0mysql> 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: 0mysql> 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)

本文讲解了关于mysql互换表中两列数据方法，更多先关内容请关注php'中文网。