SQL Server : how to group only part of the syntax - sql

Question

I have a problem creating a SQL Server query.
In summary, the query should get columns that are sum and count, grouped by customerID, and another column that is a case when by a column that is not used as a grouper column.
My problem is to group only part of the syntax, while the case when column does not need to be grouped.
A sample data, Test:
customerID, 1,2,3,4...
InvoiceID, 1234551, 1234552...
ProductID, A, B, C...
Date, Datetime
Income, int
customerID
InvoiceID
ProductID
Date
Income
1
1234551
A
01/01/2015
300
2
1234552
B
02/01/2016
300
I have a solution, but I am sure there is a more simple solution.
SELECT DISTINCT
Test.CustomerId,
ISNULL(TBL.Income_2015, 0) AS Income_2015,
ISNULL(TBL_2.Income_2016, 0) AS Income_2016,
CASE
WHEN Test.ProductID = 'A'
THEN 'TRUE'
ELSE 'FALSE'
END AS 'purchase_product_A',
TBL_3.Invoices
FROM
Test
LEFT OUTER JOIN
(SELECT CustomerId, SUM(Income) AS Income_2015
FROM Test
WHERE YEAR(Date) = 2015
GROUP BY CustomerId) TBL ON Test.customerID = TBL.customerID
LEFT OUTER JOIN
(SELECT CustomerId, SUM(Income) AS Income_2016
FROM Test
WHERE YEAR(Date) = 2016
GROUP BY CustomerId) TBL_2 ON Test.customerID = TBL_2.customerID
LEFT OUTER JOIN
(SELECT CustomerId, COUNT(InvoiceID) AS Invoices
FROM Test
GROUP BY CustomerId) TBL_3 ON Test.customerID = TBL_3.customerID
To produce:
customerID, 1,2,3...
Income_2015, int
Income_2016, int
Invoices, int
Purchase_product_A, boolean
customerID
Income_2015
Income_2016
Invoices
Purchase_product_A
1
300
300
2
TRUE
10
0
400
1
FALSE
Thanks!
Nir

Answer 1

You may use conditional aggregation with a single pass query:
SELECT
CustomerId,
SUM(CASE WHEN YEAR(Date) = 2015 THEN Income ELSE 0 END) AS Income_2015,
SUM(CASE WHEN YEAR(Date) = 2016 THEN Income ELSE 0 END) AS Income_2016,
COUNT(InvoiceID) AS Invoices,
CASE WHEN COUNT(CASE WHEN ProductID = 'A' THEN 1 END) > 0
THEN 'TRUE' ELSE 'FALSE' END AS [Purchase_product_A]
FROM Test
GROUP BY
CustomerId;