SQL Server 2014 UDF - Streamlining Function - tsql

Question

I'm a novice who started self-teaching SQL/T-SQL. I've been working with SQL 2014 Express and trying to do everything by writing T-SQL scripts. I'm doing this to help a friend with a database for her live action game she is writing, and can use some help in terms of making the following user defined function more streamlined/write it in a more correct manner.
The function itself I believed necessary because of the need for a persistent calculation to determine an item's economic value. This seemed like the better route than trying to do some sort of update script that updated all the values every time the Items table was updated. Sorry if this all seems rudimentary, trying to learn.
Below is the code. I have it working, I've got it in my development database and it does what it's supposed to. But I'd like to clean it up, and I'm not sure how to do that.
CREATE FUNCTION dbo.ValueCalc (#itemid int)
RETURNS INT
AS
BEGIN
declare #rm1 int, #rm1amount int, #rm1value int,
#rm2 int, #rm2amount int, #rm2value int,
#rm3 int, #rm3amount int, #rm3value int,
#rm4 int, #rm4amount int, #rm4value int,
#cm1 int, #cm1amount int, #cm1value int,
#cm2 int, #cm2amount int, #cm2value int,
#cm3 int, #cm3amount int, #cm3value int,
#cm4 int, #cm4amount int, #cm4value int,
#productionvalue int;
select #rm1 = MatReqs.RM1 FROM MatReqs WHERE MatReqs.ItemId = #itemid;
select #rm1amount = MatReqs.RM1Amount FROM MatReqs WHERE MatReqs.ItemId = #itemid;
select #rm1value = RawMats.BaseValue FROM RawMats WHERE RawMats.RawMatId = #rm1;
if (#rm1 IS NULL) set #rm1=0;
if (#rm1amount IS NULL) set #rm1amount=0;
if (#rm1value IS NULL) set #rm1value=0;
{Repeat the above 3 more times, for rm2, rm3, and rm4}
select #cm1 = MatReqs.CM1 FROM MatReqs WHERE MatReqs.ItemId = #itemid;
select #cm1amount = MatReqs.CM1Amount FROM MatReqs WHERE MatReqs.ItemId = #itemid;
select #cm1value = Items.ProdValue FROM Items WHERE Items.ItemId = #cm1;
if (#cm1 IS NULL) set #cm1=0;
if (#cm1amount IS NULL) set #cm1amount=0;
if (#cm1value IS NULL) set #cm1value=0;
{same here, just removed the repetitions}
set #productionvalue = (#rm1amount * #rm1value)
+ (#rm2amount * #rm2value)
+ (#rm3amount*#rm3value)
+ (#rm4amount*#rm4value)
+ (#cm1amount*#cm1value)
+ (#cm2amount*#cm2value)
+ (#cm3amount*#cm3value)
+ (#cm4amount*#cm4value);
set #productionvalue = #productionvalue + (#productionvalue * .15);
return #productionvalue;
END
GO

Answer 1

If I had some sample data and your desired results and your entire function, I could write a more efficient solution as SQL Server is optimized for set-based code and you don't really use it. As far as simply cleaning up, you could do this, but I'd rather you post what sample data and desired results and for me to get you a good set-based solution instead.
CREATE FUNCTION dbo.ValueCalc (#itemid INT)
RETURNS INT
AS
BEGIN
DECLARE #rm1 INT, #rm1amount INT, #rm1value INT,
#rm2 INT, #rm2amount INT, #rm2value INT,
#rm3 INT, #rm3amount INT, #rm3value INT,
#rm4 INT, #rm4amount INT, #rm4value INT,
#cm1 INT, #cm1amount INT, #cm1value INT,
#cm2 INT, #cm2amount INT, #cm2value INT,
#cm3 INT, #cm3amount INT, #cm3value INT,
#cm4 INT, #cm4amount INT, #cm4value INT,
#productionvalue INT;
--They both come from the same table with the where clause so just combine them
SELECT #rm1 = ISNULL(MatReqs.RM1,0),
#rm1amount = ISNULL(MatReqs.RM1Amount,0)
FROM MatReqs
WHERE MatReqs.ItemId = #itemid;
SELECT #rm1value = ISNULL(RawMats.BaseValue,0) F
FROM RawMats
WHERE RawMats.RawMatId = #rm1;
--The ISNULL() function will take care of this
--if (#rm1 IS NULL) set #rm1=0;
--if (#rm1amount IS NULL) set #rm1amount=0;
--if (#rm1value IS NULL) set #rm1value=0;
--Combine the first two statements again
SELECT #cm1 = ISNULL(MatReqs.CM1,0),
#cm1amount = ISNULL(MatReqs.CM1Amount,0)
FROM MatReqs
WHERE MatReqs.ItemId = #itemid;
SELECT #cm1value = ISNULL(Items.ProdValue,0)
FROM Items
WHERE Items.ItemId = #cm1;
--Again just use ISNULL
--if (#cm1 IS NULL) set #cm1=0;
--if (#cm1amount IS NULL) set #cm1amount=0;
--if (#cm1value IS NULL) set #cm1value=0;