Add a given value from a column based on the value from another column

I'm trying to generate a cars sales report using T-SQL.

The report must be grouped and ordered by Customer and Period (format M/yyyy)

The report result table must have the following columns:

Customer: The customer who bought the vehicle.
Period: the date of sale.
Cars quantity: The quantity of vehicles sold for that customer in that period, which type is Car.
Cars total price: The sum of the prices of vehicles (with Car type) sold to that customer in that period.
Trucks quantity: the quantity of vehicles sold for that customer in that period, which type is Truck.
Trucks total price: the sum of the prices of vehicles (with Truck type) sold to that customer in that period.

You can find the SQL scripts I used to create and seed the database as well as the query I'm using here: https://dbfiddle.uk/wxFrkPuK

Here's the query I'm using in attempt to generate the report:

SELECT 
    c.Name_Customer AS 'Customer', 
    FORMAT(v.Sell_Date, 'M/yyyy') AS 'Period',
    CASE 
        WHEN t.Name_Vehicle_Type = 'Car' 
            THEN (COUNT(v.ID_Vehicle)) 
            ELSE NULL 
    END AS 'Cars quantity',
    CASE
        WHEN t.Name_Vehicle_Type = 'Car' 
            THEN SUM(v.Sell_Price) 
            ELSE NULL 
    END AS 'Cars total price',
    CASE 
        WHEN t.Name_Vehicle_Type = 'Truck' 
            THEN (COUNT(v.ID_Vehicle)) 
            ELSE NULL 
    END AS 'Trucks quantity',
    CASE
        WHEN t.Name_Vehicle_Type = 'Truck' 
            THEN SUM(v.Sell_Price) 
            ELSE NULL 
    END AS 'Trucks total price'
FROM
    Customer AS c, Vehicle AS v, Vehicle_Type AS t
WHERE 
    c.ID_Customer = v.ID_Customer 
    AND v.ID_Vehicle_Type = t.ID_Vehicle_Type
GROUP BY 
    v.ID_Customer, FORMAT(v.Sell_Date, 'M/yyyy'), 
    c.Name_Customer, v.ID_Customer, t.Name_Vehicle_Type
HAVING 
    (t.Name_Vehicle_Type = 'Car' OR t.Name_Vehicle_Type = 'Truck')
ORDER BY  
    c.Name_Customer, 'Period'

Here's what I get when running the query:

Customer	Period	Cars qnt	Cars total price	Trucks qnt	Trucks total price
Jane Doe	2/2023	2	53000.00	NULL	NULL
Jane Doe	2/2023	NULL	NULL	2	380000.00
Jane Doe	4/2023	2	27000.00	NULL	NULL
Jane Doe	4/2023	NULL	NULL	2	137990.00
Jason St	5/2023	2	72500.00	NULL	NULL
Jason St	5/2023	NULL	NULL	2	330000.00
Jason St	8/2023	1	25000.00	NULL	NULL
Jason St	8/2023	NULL	NULL	1	57990.00
Mike Fen	6/2023	3	93500.00	NULL	NULL
Mike Fen	6/2023	NULL	NULL	2	330000.00

But I was expecting to receive:

Customer	Period	Cars qnt	Cars total price	Trucks qnt	Trucks total price
Jane Doe	2/2023	2	53000.00	2	380000.00
Jane Doe	4/2023	2	27000.00	2	137990.00
Jason St	5/2023	2	72500.00	2	330000.00
Jason St	8/2023	1	25000.00	1	57990.00
Mike Fen	6/2023	3	93500.00	2	330000.00

Can you see the problem? It's generating an extra line with NULL values in certain cells. I wish to mix the two lines grouping by the customer and period as shown above.

Solution

You need to remove Name_Vehicle_Type from the grouping, and instead use conditional aggregation.

Also:

Use explicit join syntax, not comma-joins, as this is much clearer and less prone to mistakes.
Use [] to quote column names, not ''.
ELSE NULL is not actually necessary, it's the default.
Use EOMONTH to group by month, not FORMAT as the strings don't sort properly and it's slow.
IN is shorter than OR although it compiles to the same thing.
Only aggregation filters should go in HAVING, otherwise use the WHERE. The server can usually push it through to the lower level, but it's best to be explicit.

SELECT
  c.Name_Customer AS Customer,
  EOMONTH(v.Sell_Date AS Period,
  COUNT(CASE WHEN t.Name_Vehicle_Type = 'Car'   THEN 1 END) AS [Cars quantity],
  SUM  (CASE WHEN t.Name_Vehicle_Type = 'Car'   THEN v.Sell_Price END) AS [Cars total price],
  COUNT(CASE WHEN t.Name_Vehicle_Type = 'Truck' THEN 1 END) AS [Trucks quantity],
  SUM  (CASE WHEN t.Name_Vehicle_Type = 'Truck' THEN v.Sell_Price END) AS [Trucks total price]
FROM Customer AS c
JOIN Vehicle AS v ON c.ID_Customer = v.ID_Customer
JOIN Vehicle_Type AS t ON v.ID_Vehicle_Type = t.ID_Vehicle_Type
WHERE t.Name_Vehicle_Type IN ('Car', 'Truck')
GROUP BY
  c.ID_Customer,
  c.Name_Customer,
  EOMONTH(v.Sell_Date)
ORDER BY
  c.Name_Customer,
  EOMONTH(v.Sell_Date);