sql server - Getting count from sql tables

Question

I have three tables in which two are master tables and other one is map. They are given below.

1. tbl_Category, having columns Id (PK) and Name

   /*

   ID      NAME
   1   Agriculture & Furtilizers
   2   Apparel & Garments
   3   Arts & Crafts   
   4   Automobiles
   

   */

2. tbl_SubCategory

   /*
   Id      SubCategoryName                       CategoryId (FK, PK of above)
   2   Badges, Emblems, Ribbons & Allied           2
   3   Barcodes, Stickers & Labels                 2
   4   Child Care & Nursery Products               2
   9   Fabrics & Textiles                      2
   
   
   
   */
   

Now the third table is tbl_Company_Category_Map, where I am holding all categories and its subcategories of a company. below is its schema and data.

/*

CompanyCategoryId   SubCategoryId   CategoryId  CompanyId
10                   36             11          1
11                   38             11          1
12                   40             11          1


*/

Above, first column is the PK of tbl_Company_Category_Map, second column is PK of tbl_SubCategory and third one is PK of tbl_Category and last one is the company id. Now what i want is to display the display total companies listed in each subcategory of a category. Somethinglike this.

Subcategory Name                                        Total COmpanies 
Apparel, Clothing & Garments                             1153
Badges, Emblems, Ribbons & Allied Products               4100
Barcodes, Stickers & Labels                              998
Child Care & Nursery Products                            2605
Cotton Bags, Canvas Bags, Jute Bags & Other Fabric Bags 2147

I am using query :

BEGIN


SELECT     tbl_SubCategory.Name AS SubCategoryName, tbl_Category.Name AS CategoryName, TotalCompanies=(Select COUNT(*) From tbl_Company_Category_Map WHERE CategoryId = @Id)
FROM         tbl_Category INNER JOIN
                      tbl_Company_Category_Map ON tbl_Category.Id = tbl_Company_Category_Map.CategoryId INNER JOIN
                      tbl_SubCategory ON tbl_Company_Category_Map.SubCategoryId = tbl_SubCategory.Id
WHERE     (tbl_Company_Category_Map.CategoryId = @Id)
Group By tbl_SubCategory.Name , tbl_Company_Category_Map.CategoryId, tbl_Category.Name 
ORDER BY tbl_Company_Category_Map.CategoryId

END

My Problem is that I am getting total number of companies same for each row. Please help me.

Answer 1

Try changing this:

TotalCompanies=(Select COUNT(*) From tbl_Company_Category_Map WHERE CategoryId = @Id)

...to this...

TotalCompanies=COUNT(*)

You are already grouping by (what I think are) the right fields, and your WHERE clause will apply the CategoryID filter for you.