如何在 sql 中创建派生属性列，它是其他两个现有列的总和

Question

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)
);

我想要一列 selling_price，它是 scost 和 dcost 的总和。

Answer 1

您可以使用 MySQL 为其生成的列。 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)

如何在 sql 中创建派生属性列，它是其他两个现有列的总和

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