An explanation of the two-column data method in mysql exchange table-Mysql Tutorial-php.cn

An explanation of the two-column data method in mysql exchange table

jacklove

Release： 2018-06-09 09:40:59

Original

2022 people have browsed it

1. Create tables and records for testing

CREATE TABLE `product` ( `id` int(10) unsigned NOT NULL AUTO_INCREMENT COMMENT &#39;产品id&#39;, `name` varchar(50) NOT NULL COMMENT &#39;产品名称&#39;, `original_price` decimal(5,2) unsigned NOT NULL COMMENT &#39;原价&#39;, `price` decimal(5,2) unsigned NOT NULL COMMENT &#39;现价&#39;, PRIMARY KEY (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;INSERT INTO `product` (`id`, `name`, `original_price`, `price`) VALUES (NULL, &#39;雪糕&#39;, &#39;5&#39;, &#39;3.5&#39;), 
(NULL, &#39;鲜花&#39;, &#39;18&#39;, &#39;15&#39;), 
(NULL, &#39;甜点&#39;, &#39;25&#39;, &#39;12.5&#39;), 
(NULL, &#39;玩具&#39;, &#39;55&#39;, &#39;45&#39;), 
(NULL, &#39;钱包&#39;, &#39;285&#39;, &#39;195&#39;);

Copy after login

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)

Copy after login

2. Exchange the values of original_price and price

Novices may use the following methods to exchange

update product set original_price=price,price=original_price;

Copy after login

But the result of this execution will only make the values of original_price and price both be the value of price, because update is sequential,
execute firstoriginal_price=price , the value of original_price has been updated to price,
Then execute price=original_price, which is equivalent to no update.

Execution result:

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)

Copy after login

The correct exchange method is as follows:

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

Copy after login

Execution results:

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)

Copy after login

This article explains the two-column data method in the mysql exchange table. For more information, please pay attention to php' Chinese website.

Related recommendations:

How to generate 0~1 random decimal method through php

About the use of mysql timestamp formatting function from_unixtime Instructions

Instructions on the use of mysql functions concat and group_concat

The above is the detailed content of An explanation of the two-column data method in mysql exchange table. For more information, please follow other related articles on the PHP Chinese website!