mysql互換表中兩列資料方法

create

table
`product` (  `id`
int(10) unsigned not
null auto_increment comment '產品id',  `name`
varchar(50) not
null comment '產品名稱',  `original_price`
decimal(5,2) unsigned not
null comment '原價',  `price`
decimal(5,2) unsigned not
null comment '現價',  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)

新手可能會使用以下方法進行互換

update product set original_price=price,price=original_price;

先執行original_price=price , original_price的值已經更新為price， 

然後執行price=original_price，這裡相當於沒有更新。

執行結果：

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

;

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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