别名表中的 MySQL 总和

Question

I have this query...

CREATE VIEW CustOrderItems AS
SELECT CustFirstName, CustLastName, OrderNumber, OrderDate, ShipDate, 
QuantityOrdered * QuotedPrice AS ItemTotal
FROM Customers NATURAL JOIN Orders NATURAL JOIN Order_Details;

After grouping the orders like this...

SELECT CustFirstName, CustLastName, OrderNumber, OrderDate, ShipDate, 
QuantityOrdered * QuotedPrice AS ItemTotal
FROM Customers NATURAL JOIN Orders NATURAL JOIN Order_Details
GROUP BY OrderNumber
ORDER BY OrderNumber ASC;

I know need to calculate the sum of all the ItemTotal's added together?

Any help is much appreciated!

Answer 1

As has been mentioned in a comment already, you get sums in SQL with SUM , which should not be much of a surprise. It seems strange you know about GROUP BY , but not about SUM .

At this point I'd like to recommend to always aggregate before joining, not afterwards. You want orders with their customer information and their total price. So select from orders, join with customers, join with total prices. Once you want aggregates from different tables, this approach will save you some trouble.

SELECT 
  c.CustFirstName,
  c.CustLastName,
  o.OrderNumber,
  o.OrderDate,
  o.ShipDate, 
  od.OrderTotal
FROM Orders o
JOIN Customers c ON c.CustomerNumber = o.CustomerNumber
JOIN 
(
  SELECT
    OrderNumber,
    SUM(QuantityOrdered * QuotedPrice) AS OrderTotal
  FROM Order_Details
  GROUP BY OrderNumber
) od ON od.OrderNumber = o.OrderNumber
ORDER BY o.OrderNumber ASC;