使用联接的SQL函数中的算术

Question

I am new to SQL. I am trying to perform some arithmetic using an SQL function.

I have three tables:

Table1

Table1_ID
Table2_ID
Value 

Table2

Table2_ID
Switch

Table3

Table3_ID
Table1_ID
Table2_ID
X_Column

I have the contents of X_Column from Table 3 as input to start with, which will be the input to my function. These are the conditions:

1) Multiple Table2_ID can have the same X_Column input and not vice versa

2) Multiple Table1_ID can have the same Table2_ID and not vice versa

3) Every X_Column input has one or more Table2_IDs; Every Table2_ID has one or more Table1_IDs

All I want to do is multiply and return the contents of the field Value from Table1, which has a Table1_ID, a corresponding Table2_ID, a corrsponding Table3_ID corresponding to an input X_Column, whenever a particular input X_Column is inputted.

I am not able to understand how to do this. I think it is possible using Joins or Views. I don't have any related code to post here yet. Could someone please help?

Answer 1

I'm guessing at the column data types...

Join the tables through the Table2_ID column. When the rows from the different tables are joined, you can multiply the columns: Table1.Value * Table3.X_Column

-- sample tables
declare @Table1 table (Table1_ID int, Table2_ID int, Value numeric(18,2));
declare @Table2 table (Table2_ID int, Switch bit);
declare @Table3 table (Table3_ID int, Table1_ID int, Table2_ID int, X_Column numeric(18,2));

-- sample data
insert @Table1 values(100, 200, 5.00);
insert @Table1 values(100, 201, 10.00);
insert @Table2 values(200, 0);
insert @Table2 values(201, 1);
insert @Table3 values(300, 100, 200, 2.0);
insert @Table3 values(300, 100, 201, 2.5);

declare @X_Column numeric(18,2);
set @X_Column = 2.0;

select
    t1.Value * t3.X_Column
from @Table1 t1
join @Table2 t2 on t2.Table2_ID = t1.Table2_ID
join @Table3 t3 on t3.Table2_ID = t2.Table2_ID
where t3.X_Column = @X_Column