How to get multiple column name from single join in sql?

Question

Not sure about the title of the question its right/wrong.

I have two tables

Category: CategoryID,CategoryName ,ParentCategoryID
ref_Product_Category: CategoryID, ProductID

I have written a query like this,

 SELECT  R.productID,
         C.ParentCategoryID,
         C.categoryName

 FROM    Category C 
         INNER JOIN ref_Product_Category R
            ON C.categoryID = R.categoryID

So it returned me 4 columns in the result, But now I want another column which will contain the ParentCategoryID's category name. I am not sure how to do it. Category table is self referencing table.

Answer 1

Try with Left outer join on the table itself (so we do not lose any rows if INNER JOIN is used and no ParentCategoryID is specified):

SELECT  R.productID,
         C.ParentCategoryID,
         C.categoryName,
         ISNULL(C1.CategoryName, '') as ParentCategoryName
 FROM    Category C 
         INNER JOIN ref_Product_Category R
            ON C.categoryID = R.categoryID
         LEFT OUTER JOIN Category C1 on Category.ParentCategoryID = C1.CategoryID

Answer 2

Try this:

 SELECT  R.productID,
         C.ParentCategoryID,
         C.categoryName,
         C.CategoryName,
         CP.CategoryName as ParentCategory
 FROM    Category C  
 INNER JOIN ref_Product_Category R ON C.categoryID = R.categoryID
 INNER JOIN Category CP ON Cp.CategoryID=C.ParentCategoryID

Answer 3

Try this one.

SELECT  R.productID,
         C.ParentCategoryID,
         C.categoryName, p.ParentCategoryName

 FROM    Category C 
         INNER JOIN ref_Product_Category R
            ON C.categoryID = R.categoryID INNER JOIN ParentCategory p on p.ParentCategoryID=c.ParentCategoryID