MySQL 如何从多列计算值

要从多列计算值，请使用GROUP BY。以下是语法 –

select yourColumnName1,sum(yourColumnName2*yourColumnName3) AS anyAliasName
from yourTableName group by yourColumnName1;

让我们首先创建一个表 –

mysql> create table calculateValueDemo
   -> (
   -> Id int,
   -> ProductPrice int,
   -> ProductWeight int
   -> );
Query OK, 0 rows affected (0.56 sec)

以下是使用insert命令向表中插入记录的查询 –

mysql> insert into calculateValueDemo values(100,35,5);
Query OK, 1 row affected (0.16 sec)

mysql> insert into calculateValueDemo values(101,50,3);
Query OK, 1 row affected (0.16 sec)

mysql> insert into calculateValueDemo values(100,100,4);
Query OK, 1 row affected (0.17 sec)

mysql> insert into calculateValueDemo values(101,500,2);
Query OK, 1 row affected (0.22 sec)

以下是使用select语句显示表中所有记录的查询 –

mysql> select * from calculateValueDemo;

这将产生以下输出 –

+------+--------------+---------------+
| Id   | ProductPrice | ProductWeight |
+------+--------------+---------------+
| 100  | 35           | 5             |
| 101  | 50           | 3             |
| 100  | 100          | 4             |
| 101  | 500          | 2             |
+------+--------------+---------------+
共 4 行 (0.00 秒)

以下是计算多列值的查询 –

mysql> select Id,sum(ProductPrice*ProductWeight) AS Total from calculateValueDemo group by Id;

这将产生以下输出 –

+------+-------+
| Id   | Total |
+------+-------+
| 100  | 575   |
| 101  | 1150  |
+------+-------+
共 2 行 (0.00 秒)

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