SQL+基礎語句（三）

1.我們希望計算 "OrderPrice" 字段的平均值

SELECT AVG(OrderPrice) AS OrderAverage FROM Orders

我們希望找到 OrderPrice 值高於 OrderPrice 平均值的客戶

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

2.我們希望計算客戶 "Carter" 的訂單數

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

3.我們希望查找 "OrderPrice" 列的第一個值

SELECT FIRST(OrderPrice) AS FirstOrderPrice FROM Orders

我們希望查找 "OrderPrice" 列的最後一個值

SELECT LAST(OrderPrice) AS LastOrderPrice FROM Orders

4.我們希望查找 "OrderPrice" 列的最大值

SELECT MAX(OrderPrice) AS LargestOrderPrice FROM Orders

5.我們希望查找 "OrderPrice" 列的最小值

SELECT MIN(OrderPrice) AS SmallestOrderPrice FROM Orders

6.我們希望查找 "OrderPrice" 字段的總數

SELECT SUM(OrderPrice) AS OrderTotal FROM Orders

7.我們希望查找每個客戶的總金額（總訂單）。我們想要使用 GROUP BY 語句對客戶進行組合

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

8.在 SQL 中增加 HAVING 子句原因是，WHERE 關鍵字無法與合計函數一起使用

我們希望查找訂單總金額少於 2000 的客戶

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