SQL+基础语句（三）

1.我们希望计算 "OrderPrice" 字段的平均值

SELECT AVG(OrderPrice) AS OrderAverage FROM Orders

我们希望找到 OrderPrice 值高于 OrderPrice 平均值的客户

SELECT Customer FROM Orders WHERE OrderPrice>(SELECT AVG(OrderPrice) FROM Orders)

2.我们希望计算客户 "Carter" 的订单数

SELECT COUNT(Customer) AS CustomerNilsen FROM Orders WHERE Customer='Carter'

3.我们希望查找 "OrderPrice" 列的第一个值

SELECT FIRST(OrderPrice) AS FirstOrderPrice FROM Orders

我们希望查找 "OrderPrice" 列的最后一个值

SELECT LAST(OrderPrice) AS LastOrderPrice FROM Orders

4.我们希望查找 "OrderPrice" 列的最大值

SELECT MAX(OrderPrice) AS LargestOrderPrice FROM Orders

5.我们希望查找 "OrderPrice" 列的最小值

SELECT MIN(OrderPrice) AS SmallestOrderPrice FROM Orders

6.我们希望查找 "OrderPrice" 字段的总数

SELECT SUM(OrderPrice) AS OrderTotal FROM Orders

7.我们希望查找每个客户的总金额（总订单）。我们想要使用 GROUP BY 语句对客户进行组合

SELECT Customer,SUM(OrderPrice) FROM Orders
GROUP BY Customer

8.在 SQL 中增加 HAVING 子句原因是，WHERE 关键字无法与合计函数一起使用

我们希望查找订单总金额少于 2000 的客户

SELECT Customer,SUM(OrderPrice) FROM Orders
GROUP BY Customer
HAVING SUM(OrderPrice)<2000