Question

This might be a little hard to explain, but I will try.

I want to display a list of categories (stored in 1 table), and number of domains associated with each category (stored in another table).

The monkey wrench in this case is that each domain has a set of records associated with it (which are stored in a 3rd table). I only want to show the categories that have domains associated with them, and the count of domains should reflect only the domains that have records associated with them (from the 3rd table).

My current query

SELECT r.rev_id, c.cat_id, c.cat_name, count(d.dom_id) As rev_id_count FROM reviews r INNER JOIN  domains d ON r.rev_domain_from=d.dom_id  INNER JOIN  categories c ON d.dom_catid=c.cat_id   WHERE rev_status = 1 GROUP BY cat_name   ORDER BY cat_name 

This selects the correct category names, but shows a false count (rev_id_count). If the category has 2 domains in it, and each domain has 2 records, it will show count of 4, when it should be 2.

Answer 1

SELECT Categories.Name,count(DISTINCT categories.name) FROM Categories JOIN Domains ON Categories.ID=Domains.CID JOIN Records ON Records.DID=Domains.ID GROUP BY Categories.Name

Tested with following setup:

 CREATE TABLE Categories (Name nvarchar(50), ID int  NOT NULL IDENTITY(1,1)) CREATE TABLE Domains (Name nvarchar(50), ID int NOT NULL IDENTITY(1,1), CID int) CREATE TABLE Records (Name nvarchar(50), ID int NOT NULL IDENTITY(1,1), DID int)  INSERT INTO Records (DID) VALUES (1) INSERT INTO Records (DID) VALUES (1) INSERT INTO Records (DID) VALUES (2) INSERT INTO Records (DID) VALUES (2) INSERT INTO Records (DID) VALUES (3) INSERT INTO Records (DID) VALUES (3)  INSERT INTO Domains (Name,CID) VALUES ('D1',1) INSERT INTO Domains (Name,CID) VALUES ('D2',1) INSERT INTO Domains (Name,CID) VALUES ('D5',1) INSERT INTO Domains (Name,CID) VALUES ('D3',2) INSERT INTO Domains (Name,CID) VALUES ('D4',2)  INSERT INTO Categories (Name) VALUES ('1') INSERT INTO Categories (Name) VALUES ('2') INSERT INTO Categories (Name) VALUES ('3')