Inner join in select statement within stored procedure

Question

I'm trying to Create a stored procedure but there is a field actually exist in another field but its id is used as foreign key in current table, SQL Query is:

Create Procedure sp_Select
As
Begin
 SELECT [ProductID]
 ,[Name]
 ,SELECT tblCategories.CategoryName 
 FROM tblCategories INNER JOIN tblProducts 
 ON tblCategories.CategoryId = tblProducts.CategoryID;
 ,[Model]
 ,Cast([RAM] As nvarchar(10)) +' '+[RAMMemUnit] As RAM
 ,Cast([SecondryMem] As nvarchar(10)) + ' ' + [SecondMemUnit] As Memory
 ,[OSVersion]
 ,[Processor]
 ,CAST([Battery] As nvarchar(10)) +' '+ [BatteryType] As Battery
 ,UnitsInStock AS 'Quantity In Stock'
 FROM [tblProducts]
End

Error in this following portion: SELECT tblCategories.CategoryName FROM tblCategories INNER JOIN tblProducts ON tblCategories.CategoryId = tblProducts.CategoryID;

Someone help me please.

Answer 1

There are actually two problems with your first query. The first is that you have an extra semi-colon for the subquery where you are getting the category name. The second is that if that query returns more than one row then you will receive an error. I've corrected it for you to eliminate both of those issues.

CREATE PROCEDURE sp_Select
AS
BEGIN
 SELECT [ProductID]
 ,[Name]
 , CategoryName = (SELECT TOP 1 tblCategories.CategoryName
 FROM tblCategories
 WHERE tblCategories.CategoryId = tblProducts.CategoryID)
 ,[Model]
 , Cast([RAM] AS NVARCHAR(10)) + ' ' + [RAMMemUnit] AS RAM
 ,Cast([SecondryMem] AS NVARCHAR(10)) + ' ' + [SecondMemUnit] AS Memory
 ,[OSVersion]
 ,[Processor]
 ,CAST([Battery] AS NVARCHAR(10)) + ' ' + [BatteryType] AS Battery
 ,UnitsInStock AS 'Quantity In Stock'
 FROM [tblProducts];
END

However, queries that have sub-queries like the above generally perform worse than ones that can achieve the same results with a sub-query. It lets you access other fields from the tblCategories table without incurring additional sub-query costs, and you can more easily search for products that are in particular categories.

Some of the comments have mentioned changing the join from using a LEFT OUTER to be an INNER join. I chose LEFT OUTER initially because that more closely matched the result set you would have received in your first query. Essentially, it would have NULL's in place where the CategoryName would be assuming you had Products without Categories. An INNER JOIN would eliminate products that had no matching category.

CREATE PROCEDURE sp_Select
AS
BEGIN
 SELECT P.[ProductID]
 ,P.[Name]
 , C.CategoryName
 ,P.[Model]
 , Cast(P.[RAM] AS NVARCHAR(10)) + ' ' + P.[RAMMemUnit] AS RAM
 ,Cast(P.[SecondryMem] AS NVARCHAR(10)) + ' ' + P.[SecondMemUnit] AS Memory
 ,P.[OSVersion]
 ,P.[Processor]
 ,CAST(P.[Battery] AS NVARCHAR(10)) + ' ' + P.[BatteryType] AS Battery
 ,P.UnitsInStock AS 'Quantity In Stock'
 FROM [tblProducts] AS P
 LEFT OUTER JOIN tblCategories AS C ON C.CategoryId = P.CategoryID;
END

• Erik Reasonable Rates Darling: I don't think there's any guarantee that replacing a subquery with a left outer join will make things faster.
• ypercubeᵀᴹ: The corrected subquery needs more correction: to become correlated. As it is, it will return more than 1 rows and throw error (unless there is only 1 product).
• Muhazzab Chouhadry: So Can you please correct it.?
• RDFozz: @MuhazzabChouhadry - The final query deals with it, by removing the subquery. The INNER JOIN provides the correlation mentioned. If you really want to use the subquery, replace INNER JOIN tblProducts ON with WHERE in the first version of the query in Jonathan's answer.
• Muhazzab Chouhadry: @RDFozz I think this is also working fine, What is the benefit of using this query.?