Northwind SQL 每个客户的订单总数

Question

我已将 TotalOrders 列添加到 Customers table。

ALTER TABLE customers ADD TotalOrders INT NULL

我正在尝试查找每个客户的订单总数并将该值添加到此列，但是我无法弄清楚我需要准确地求和什么

INSERT INTO customers (TotalOrders) SELECT SUM(...)

Answer 1

INSERT INTO customers (TotalOrders) 
VALUES(SELECT SUM(Orders.Total)  
FROM Orders INNER JOIN Customers ON Orders.CustomerId=
Customer.Id Group By  Customer.Id) WHERE Customer.Id =Orders.CustomerId

Answer 2

我认为您应该在这里使用更新。您可以在 orders table 中汇总每个客户的订单总数，然后使用此信息更新 customers table。

UPDATE t1
SET TotalOrders = t2.TotalOrders
FROM customers t1
INNER JOIN
(
    SELECT CustomerID, COUNT(*) AS TotalOrders
    FROM orders
    GROUP BY CustomerID
) t2
    ON t1.CustomerID = t2.CustomerID

Northwind SQL 每个客户的订单总数

Northwind SQL total orders per customer

sql

sql-server

northwind