how to calculate column to other table - sql-server

Question

i want to make column Customers_Balance on TBL_CUSTOMERS to show by defult the result of that stored procedures....
TBL_CUSTOMERS which it have the info of the customer, and it created as like that
CREATE TABLE TBL_CUSTOMERS
(
Customers_ID int PRIMARY KEY,
Customers_Name varchar(100) NOT NULL,
Customers_Phone varchar(100),
Customers_Address varchar(100),
Customers_Web varchar(100),
Customers_Balance decimal(16,0) not null,
);
TBL_CUSTOMERS_DETAILS which it have the details of all customer transactions , and it created as like that
CREATE TABLE TBL_CUSTOMERS_DETAILS
(
Customers_Details_ID int PRIMARY KEY,
Customers_ID int,
Customers_Details_Tybe varchar(50) not null,
Customers_Details_Date date not null,
Customers_Details_Amount decimal(16,0) not null,
);
i have created stored procedures to calculate the result of sum of customer's transactions balance and worked fine, and it created as like that
CREATE PROC SP_SUM_CUSTOMERS_DETAILS_AMOUNT
#ID INT
AS
SELECT SUM(Customers_Details_Amount)
FROM TBL_CUSTOMERS_DETAILS
Where Customers_ID = #ID
NOW
i want to make column Customers_Balance on TBL_CUSTOMERS to show by defult the result of that stored procedures....
how i can make something like that ??

Answer 1

Materializing values that can be calculated by other materialize values is usually a bad idea as it bears the risk of inconsistencies.
So you best drop the column Customers_Balance in TBL_CUSTOMERS and the procedure and then create a view which includes the customer's data and their balance. You can do so by a join and aggregation.
ALTER TABLE TBL_CUSTOMERS
DROP COLUMN Customers_Balance;
DROP PROCEDURE SP_SUM_CUSTOMERS_DETAILS_AMOUNT;
CREATE VIEW VW_CUSTOMERS
AS
SELECT C.Customers_ID,
C.Customers_Name,
C.Customers_Phone,
C.Customers_Address,
C.Customers_Web,
sum(CD.Customers_Details_Amount) Customers_Balance
FROM TBL_CUSTOMERS C
INNER JOIN TBL_CUSTOMERS_DETAILS CD
ON CD.Customers_ID = C.Customers_ID
GROUP BY C.Customers_ID,
C.Customers_Name,
C.Customers_Phone,
C.Customers_Address,
C.Customers_Web;

Answer 2

You are looking for a Computed Column
What you need to do is to create a scalar function rather than a stored procedure (simply change your current stored procedure into a scalar function), and then use this function in your computed column. This would give you an auto-updated results on your computed column.
So, redoing your work should be something like this :
-- CREATE THE SCALAR FUNCTION FIRST
CREATE FUNCTION SUM_CUSTOMERS_DETAILS_AMOUNT (#ID INT)
RETURNS INT
AS
BEGIN
RETURN (
SELECT SUM(Customers_Details_Amount)
FROM TBL_CUSTOMERS_DETAILS
WHERE Customers_ID = #ID
)
END
GO
-- NOW DROP THE CURRENT Customers_Balance COLUMN
ALTER TABLE TBL_CUSTOMERS
DROP COLUMN Customers_Balance
GO
-- CREATE THE COMPUTED COLUMN WITH THE FUNCTION
ALTER TABLE TBL_CUSTOMERS
ADD Customers_Balance AS dbo.SUM_CUSTOMERS_DETAILS_AMOUNT (Customers_ID)
GO