SQL combining multiple select statements into a single query - sql

Question

I have the following query which gets the total outstanding invoices and removed the total payments and credit notes to get the outstanding balance.
declare #tInv decimal(19, 2)
declare #tCrn decimal(19, 2)
declare #tPay decimal(19, 2)
set #tInv =
(
SELECT SUM(ST_Unallocated) from Transactions where ST_COPYCUST = 'LOEH001' and ST_TRANTYPE = 'INV'
)
set #tCrn =
(
SELECT SUM(ST_Unallocated) from Transactions where ST_COPYCUST = 'LOEH001' and ST_TRANTYPE = 'CRN'
)
set #tPay =
(
SELECT SUM(ST_Unallocated) from Transactions where ST_COPYCUST = 'LOEH001' and ST_TRANTYPE = 'PAY'
)
declare #currBal decimal(19, 2)
set #currBal =
(
SELECT #tInv - #tPay - #tCrn
)
select #currBal
I want to combine the above query with the below query to show the total outstanding balance for each customer -
select
c.AccountNumber,
c.CustomerID,
c.FullName,
ct.Description as 'CustomerTypeDesc',
c.TelNumber,
c.EmailAddress
from Customers c
inner join CustomerTypes ct on c.CustomerType = ct.TypeID
left join Transactions t on c.AccountNumber = ST_COPYCUST
where c.StatusID = 0 or c.StatusID = 1
Any ideas how I can do this?
Thanks

Answer 1

Try the following query. I have made a few assumptions and have removed the join on the Transactions table from your primary query as I think this is surplus to requirements. The beauty of using these inline queries is that you can return more than one customer if required (by removing the filter on c.AccountNumber):
SELECT
c.AccountNumber
, c.CustomerID
, c.FullName
, ct.Description as 'CustomerTypeDesc'
, c.TelNumber
, c.EmailAddress
, (SELECT SUM(ST_Unallocated) from Transactions where ST_COPYCUST = c.AccountNumber and ST_TRANTYPE = 'INV') -
(SELECT SUM(ST_Unallocated) from Transactions where ST_COPYCUST = c.AccountNumber and ST_TRANTYPE = 'CRN') -
(SELECT SUM(ST_Unallocated) from Transactions where ST_COPYCUST = c.AccountNumber and ST_TRANTYPE = 'PAY') AS BalanceToPay
FROM Customers c
INNER JOIN CustomerTypes ct on c.CustomerType = ct.TypeID
WHERE c.StatusID IN (0,1) AND c.AccountNumber = ST_COPYCUST

Answer 2

Hope didn't broke it, should be faster than with subqueries:
SELECT
c.AccountNumber
, c.CustomerID
, c.FullName
, ct.Description as 'CustomerTypeDesc'
, c.TelNumber
, c.EmailAddress
, SUM(CASE WHEN ST_TRANTYPE = 'INV' THEN t.ST_Unallocated ELSE 0 END) AS tInv
, SUM(CASE WHEN ST_TRANTYPE = 'CRN' THEN t.ST_Unallocated ELSE 0 END) AS tCRN
, SUM(CASE WHEN ST_TRANTYPE = 'PAY' THEN t.ST_Unallocated ELSE 0 END) AS tPAY
, SUM(CASE WHEN ST_TRANTYPE = 'INV' THEN t.ST_Unallocated ELSE 0 END) -
SUM(CASE WHEN ST_TRANTYPE = 'PAY' THEN t.ST_Unallocated ELSE 0 END) -
SUM(CASE WHEN ST_TRANTYPE = 'CRN' THEN t.ST_Unallocated ELSE 0 END) as currBal
FROM Customers c
INNER JOIN CustomerTypes ct on c.CustomerType = ct.TypeID
LEFT JOIN Transactions t on c.AccountNumber = t.ST_COPYCUST
WHERE c.StatusID = 0 or c.StatusID = 1 AND c.AccountNumber = ST_COPYCUST
GROUP BY c.AccountNumber
, c.CustomerID
, c.FullName
, ct.Description
, c.TelNumber
, c.EmailAddress