如何在sql中创建一个派生属性列，它是其他两个现有列的总和

Posted 2023-02-16

【中文标题】如何在sql中创建一个派生属性列，它是其他两个现有列的总和

【英文标题】：How to create a derived attribute column in sql which is sum of other two existing columns

【发布时间】：2021-11-14 17:05:12

【问题描述】：

CREATE TABLE Software
(
    name varchar(8) not null,
    title varchar(20) not null,
    dev_in varchar(8) not null,
    scost decimal(7,2),
    dcost integer(5),
    sold integer(3)
);

我想要一个列 sell_price，它是 scost 和 dcost 的总和。

【参考方案1】：

您可以使用 mysql 生成的列。 Reference Doc

-- when creating table

create table software ( 
  name varchar(8) not null,
  title varchar(20) not null, 
  dev_in varchar(8) not null, 
  scost decimal(7,2), 
  dcost integer(5), 
  sold integer(3), 
  selling_price decimal(7,2) as (dcost + scost) 
);

-- or for an existing table

alter table software add column selling_price decimal(7,2) as (dcost + scost);

mysql> insert into software (name, title, dev_in, scost, dcost, sold)
    -> values("s", "s", "ss", 100.1, 2, 3);

mysql> select * from software;
+------+-------+--------+--------+-------+------+---------------+
| name | title | dev_in | scost  | dcost | sold | selling_price |
+------+-------+--------+--------+-------+------+---------------+
| s    | s     | ss     | 100.10 |     2 |    3 |       102.10  |
+------+-------+--------+--------+-------+------+---------------+
1 row in set (0.00 sec)