View query without sub selecting T-SQL - tsql

Question

so I'm trying to build a view query but I keep failing using only joins so I ended up with this deformation.. Any tips on how I can write this query so I don't have to use 6 subselects?
The FeeSum and PaymentSum can be null, so ideally I do not want those in my result set and I also wouldn't like results where the FeeSum and the PaymentSum are equal.
Quick note: client is the table where the clients informations are stored (name, adress, etc..)
customer has a fk on client and is kind of a shell table for the client that store more information for the client,
payment is a list of all payments a customer did,
order is a list of all orders a customer did.
The goal is to get a list where we can track which customer has open fees to pay, based on the orders. It's a legacy project so don't ask why people can order before paying :)
SELECT
cu.Id as [CustomerId]
, CASE
WHEN cl.IsPerson = 1
THEN cl.[AdditionalName] + ' ' + cl.[Name]
ELSE cl.AdditionalName
END as [Name]
, cl.CustomerNumber
, (SELECT SUM(o.Fee) FROM [publication].[Order] o WHERE o.[State] = 2 AND o.CustomerId = cu.Id) as [FeeSum]
, (SELECT SUM(p.Amount) FROM [publication].[Payment] p WHERE p.CustomerId = cu.Id) as [PaymentSum]
, (SELECT MAX(o.OrderDate) FROM [publication].[Order] o WHERE o.[State] = 2 AND o.CustomerId = cu.Id) as [LastOrderDate]
, (SELECT MAX(p.PaymentDate) FROM [publication].[Payment] p WHERE p.CustomerId = cu.Id) as [LastPaymentDate]
, (SELECT MAX(f.Created) FROM [client].[File] f WHERE f.TemplateName = 'Reminder' AND f.ClientId = cl.Id) as [LastReminderDate]
, (SELECT MAX(f.Created) FROM [client].[File] f WHERE f.TemplateName = 'Warning' AND f.ClientId = cl.Id) as [LastWarningDate]
FROM
[publication].[Customer] cu
JOIN
[client].[Client] cl
ON cl.Id = cu.ClientId
WHERE
cu.[Type] = 0
Thanks in advance and I hope I didn't do anything wrong.
Kind regards

Answer 1

You could rewrite the correlated subqueries to instead use joins:
SELECT
cu.Id AS [CustomerId],
CASE WHEN cl.IsPerson = 1
THEN cl.[AdditionalName] + ' ' + cl.[Name]
ELSE cl.AdditionalName END AS [Name],
cl.CustomerNumber,
o.FeeSum,
p.PaymentSum,
o.LastOrderDate,
p.LastPaymentDate,
f.LastReminderDate,
f.LastWarningDate
FROM [publication].[Customer] cu
INNER JOIN [client].[Client] cl
ON cl.Id = cu.ClientId
INNER JOIN
(
SELECT CustomerId, SUM(Fee) AS [FeeSum], MAX(OrderDate) AS [LastOrderDate]
FROM [publication].[Order]
WHERE o.[State] = 2
GROUP BY CustomerId
) o
ON o.CustomerId = cu.Id
INNER JOIN
(
SELECT CustomerId, SUM(Amount) AS [PaymentSum], MAX(PaymentDate) AS [LastPaymentDate]
FROM [publication].[Payment]
WHERE o.[State] = 2
GROUP BY CustomerId
) p
ON p.CustomerId = cu.Id
INNER JOIN
(
SELECT ClientId,
MAX(CASE WHEN TemplateName = 'Reminder' THEN Created END) AS [LastReminderDate],
MAX(CASE WHEN TemplateName = 'Warning' THEN Created END) AS [LastWarningDate]
FROM [client].[File]
GROUP BY ClientId
) f
ON f.ClientId = cl.Id
WHERE
cu.[Type] = 0;