Fetch rows and count them in sqlserver - sql

Question

I wrote a stored procedure that join three tables to fetch province title from it's table. This is my code:
BEGIN
select TbProvince.title, count(TbProvince.title) as cnt
from TbProvince
where TbProvince.provinceId IN (select TbCustomerUser.provinceId
from TbCustomerUser INNER JOIN
TbDeals
on TbCustomerUser.UserId = TbDeals.sellerUserID
where TbDeals.buyerUserID = 1
)
group by TbProvince.title
end
Description: I have three tables for deals, customers and provinces. I want to retrieve province title and the count of that for customers that were sellers.
The above code have no problem, but only return 1 as a count. The number of customers is more than one.
Can anybody help me solve my problem?

Answer 1

Your query is filtering the rows of TbProvince and then aggregating that table -- and only that table.
Instead, you want to join the tables together to count the customers not the provinces. The query is much simpler to write and read if you use table aliases:
select p.Title, count(*)
from TbCustomerUser cu join
TbDeals d
on cu.UserId = d.sellerUserID join
TbProvince p
on p.provinceId = cu.provinceId
where d.buyerUserID = 1
group by p.Title;

Answer 2

You have to perform the JOIN with customer table. If you use semi join (expressed by IN construct in your case) then you avoid duplicates that are expected in your case.
SELECT TbProvince.title,
COUNT(TbProvince.title) AS cnt
FROM TbProvince
JOIN TbCustomerUser ON TbProvince.provinceId = TbCustomerUser.provinceId
JOIN TbDeals ON TbCustomerUser.UserId = TbDeals.sellerUserID
WHERE TbDeals.buyerUserID = 1
GROUP BY TbProvince.title;

Answer 3

It should be as simple as:
You won't need the subselect. Just join all three tables and you'll receive your desired result.
SELECT TbProvince.title,
count(TbProvince.title) as cnt
FROM TbProvince
INNER JOIN TbCustomerUser
ON TbProvince.provinceId = TbCustomerUser.provinceId
INNER JOIN TbDeals
ON TbCustomerUser.UserId = TbDeals.sellerUserID
AND TbDeals.buyerUserID = 1
GROUP BY TbProvince.title
Why did your solution not work?
You subselect will return a "list" of provinceIDs from TbCustomerUser combinated with TbDeals with your restriction TbDeals.buyerUserID = 1.
The outer select will now return all rows from TbProvince IN this list.
But it's not returning a row for each Customer who had a deal.
That's why you have to JOIN all three tables at once.