Best way to aggregate data - Update query or subquery? - sql-server

Question

I'm trying to aggregate some customer order data into one table for analysis. The data is the number of products a customer orders, then trying to determine whether the order is a small, medium, or large order, then determine the total products they bought and the cost of the order by OrderSize.
Small order - 1 - 2 products
Medium order - 3 - 4 products
Large Order - >=5 products
Here is the data:
CustomerID OrderID OrderSize OrderTotal
1 800 1 $20
2 801 1 $10
3 802 4 $85
1 803 1 $30
2 804 8 $120
3 805 1 $40
Here is the table I am attempting to build (easier to just post an image):
I could run an update query like this to populate the table:
-- Build the table --
CREATE TABLE Customers (
CustomerID varchar(10) PRIMARY KEY,
SmallOrderCount int,
SmallOrderProducts int,
SmallOrderTotal money,
MedOrderCount int,
MedOrderProducts int,
MedOrderTotal money,
LargeOrderCount int,
LargeOrderProducts int,
LargeOrderTotal money
);
-- Insert the unique customers --
INSERT INTO Customers
SELECT CustomerID FROM Orders GROUP BY CustomerID;
-- Update to populate the order information --
UPDATE Customers
SET SmallOrderCount = (SELECT count(*) FROM Orders WHERE OrderSize BETWEEN 1 AND 2 AND Orders.CustomerID = Customers.CustomerID);
UPDATE Customers
SET SmallOrderProducts = (SELECT sum(OrderSize) FROM Orders WHERE OrderSize BETWEEN 1 AND 2 AND Orders.CustomerID = Customers.CustomerID);
UPDATE Customers
SET SmallOrderTotal = (SELECT sum(OrderTotal) FROM Orders WHERE OrderSize BETWEEN 1 AND 2 AND Orders.CustomerID = Customers.CustomerID);
Then I could repeat this for the remaining 6 columns.
However, this seems like a lot of work. Is there a way to populate my Customer table using a subquery that may be less work? Or is my approach above the most direct?

Answer 1

You can do all of it in one INSERT command with CASE statements:
INSERT INTO Customers
SELECT CustomerID
,sum(CASE WHEN OrderSize BETWEEN 1 AND 2 THEN 1 ELSE 0 END) AS SmallOrderCount
,sum(CASE WHEN OrderSize BETWEEN 1 AND 2 THEN OrderSize ELSE 0 END) AS SmallOrderProducts
,sum(CASE WHEN OrderSize BETWEEN 1 AND 2 THEN OrderTotal ELSE 0 END) AS SmallOrderTotal
,sum(CASE WHEN OrderSize BETWEEN 3 AND 4 THEN 1 ELSE 0 END) AS MedOrderCount
,sum(CASE WHEN OrderSize BETWEEN 3 AND 4 THEN OrderSize ELSE 0 END) AS MedOrderProducts
,sum(CASE WHEN OrderSize BETWEEN 3 AND 4 THEN OrderTotal ELSE 0 END) AS MedOrderTotal
,sum(CASE WHEN OrderSize > 4 THEN 1 ELSE 0 END) AS LargeOrderCount
,sum(CASE WHEN OrderSize > 4 THEN OrderSize ELSE 0 END) AS LargeOrderProducts
,sum(CASE WHEN OrderSize > 4 THEN OrderTotal ELSE 0 END) AS LargeOrderTotal
FROM Orders
GROUP BY CustomerID;
See this working demo for the full query on data.SE.

Answer 2

One insert should be enough:
INSERT INTO Customers(CustomerID,SmallOrderCount,SmallOrderProducts,
SmallOrderTotal)
SELECT a.CustomerID, COUNT(a.*) as cnt, sum(a.OrderSize) as OrderSize,
sum(a.OrderTotal) as OrderTotal
FROM Orders a
WHERE a.OrderSize BETWEEN 1 AND 2
GROUP BY a.CustomerID
The query above will insert only customers whose order size is between 1 and 2. If you need to insert others as well, you can use :
INSERT INTO Customers(CustomerID,SmallOrderCount,SmallOrderProducts,
SmallOrderTotal)
SELECT a.CustomerID,
COUNT(CASE WHEN a.OrderSize BETWEEN 1 AND 2 THEN 1 END) as cnt,
sum(CASE WHEN a.OrderSize BETWEEN 1 AND 2 THEN a.OrderSize ELSE 0 END) as OrderSize,
sum(CASE WHEN a.OrderSize BETWEEN 1 AND 2 THEN a.OrderTotal ELSE 0 END ) as OrderTotal
FROM Orders a
GROUP BY a.CustomerID

Answer 3

I'd only create a single query (which can be used as view) for that and not a whole new persisted table.
WITH cteOrders AS (
SELECT CustomerID,
CASE WHEN OrderSize BETWEEN 1 AND 2 THEN OrderSize END SmallOrderProducts,
CASE WHEN OrderSize BETWEEN 1 AND 2 THEN OrderTotal END SmallOrderTotal,
CASE WHEN OrderSize BETWEEN 3 AND 4 THEN OrderSize END MediumOrderProducts,
CASE WHEN OrderSize BETWEEN 3 AND 4 THEN OrderTotal END MediumOrderTotal,
CASE WHEN OrderSize > 4 THEN OrderSize END LargeOrderProducts,
CASE WHEN OrderSize > 4 THEN OrderTotal END LargeOrderTotal
FROM Orders
)
SELECT CustomerID,
COUNT(SmallOrderProducts) SmallOrderCount,
COALESCE(SUM(SmallOrderProducts), 0) SmallOrderProducts,
COALESCE(SUM(SmallOrderTotal), 0) SmallOrderTotal,
COUNT(MediumOrderProducts) MediumOrderCount,
COALESCE(SUM(MediumOrderProducts), 0) MediumOrderProducts,
COALESCE(SUM(MediumOrderTotal), 0) MediumOrderTotal,
COUNT(LargeOrderProducts) LargeOrderCount,
COALESCE(SUM(LargeOrderProducts), 0) LargeOrderProducts,
COALESCE(SUM(LargeOrderTotal), 0) LargeOrderTotal
FROM cteOrders
GROUP BY CustomerID

Answer 4

You can do this by using single INSERT INTO SELECT statement
INSERT INTO Customers
SELECT * ,
(SELECT count(*) FROM Orders WHERE OrderSize BETWEEN 1 AND 2 AND Orders.CustomerID = CustomerID),
(SELECT sum(OrderSize) FROM Orders WHERE OrderSize BETWEEN 1 AND 2 AND Orders.CustomerID = CustomerID)
FROM CUSTOMERS