Add column name as parameter in stored procedure not working - sql-server

Question

I have a stored procedure where I want to add a column name as a parameter.
The procedure updates some columns like this.
UPDATE Reservedele
SET Bemærkning = #Bemærkning
,Art = #Art
,Type = #Type
,Lev = #Lev
,#stockNumber = #stockCount
WHERE Varenummer = #Varenummer
I want to update a column named as stock1 as I pass in as #StockNumber, but all it does is setting #stockNumber equal to #Varenummer. (Which probably what I am telling it to do).
How can I do this?
I am new to SQL and I need to read up on dynamic SQL.
My full code looks like this, but the update statement is not doing anything.
ALTER PROCEDURE [dbo].[updateItemsInSqlNoImage]
#Bemærkning nvarchar(200),
#Varenummer nchar(20),
#Art nvarchar(50),
#Type nvarchar(50),
#Lev nvarchar(50),
#Bruger nvarchar(50),
#Dato nvarchar(50),
#Tid nvarchar(50),
#Ip nvarchar(50),
#stockCount int,
#stockNumber varchar(10)
as
BEGIN
DECLARE #SQL nvarchar(MAX),
#CRLF nchar(2) = NCHAR(13) + NCHAR(10);
SET #SQL = N'UPDATE Reservedele' + #CRLF+
N',Bemærkning=#Bemærkning'+ #CRLF+
N',Art=#Art' + #CRLF+
N',Type=#Type' + #CRLF+
N',Lev=#Lev'+ #CRLF+
N' ,' + QUOTENAME(#stockNumber) + N' = #stockCount' + #CRLF +
N'WHERE Varenummer=#Varenummer;';
INSERT INTO Ændrede_dele(Varenummer,Dato,Tid,Bruger,Ip)
VALUES (#Varenummer,#Dato,#Tid,#Bruger,#stockNumber)
END

Answer 1

That isn't how SQL works, it isn't a scripting language, it's a query language. A variable cannot be used to replace a something that needs to be a literal value. #stockNumber is being seen as the parameter #stockNumber, not the value of the parameter, #stockNumber. As a result it makes it look like you have a SET operation that is part of an UPDATE but also trying to assign the value of variables/parameters (which you can't do).
You would need to use dynamic SQL to achieve this:
--All data types are guessed, replace appropriately
CREATE PROC dbo.YourProc #Bemærkning varchar(10),
#Art int,
#Type int,
#Lev decimal(6,2),
#stockNumber sysname, --apart from this one, this is correct
#stockCount int,
#Varenummer varchar(25) AS
BEGIN
DECLARE #SQL nvarchar(MAX),
#CRLF nchar(2) = NCHAR(13) + NCHAR(10);
SET #SQL = N'UPDATE Reservedele' + #CRLF +
N'SET Bemærkning = #Bemærkning' + #CRLF +
N' ,Art = #Art' + #CRLF +
N' ,Type = #Type' + #CRLF +
N' ,Lev = #Lev' + #CRLF +
N' ,' + QUOTENAME(#stockNumber) + N' = #stockCount' + #CRLF +
N'WHERE Varenummer = #Varenummer;';
--PRINT #SQL; --Your debugging friend
--Again, all data types are guessed, replace appropriately
EXEC sys.sp_executesql #SQL, N'#Bemærkning varchar(10), #Art int, #Type int, #Lev decimal(6,2), #stockCount int, #Varenummer varchar(25)', #Bemærkning, #Art, #Type, #Lev, #stockCount, #Varenummer;
END;