SQL Functions

COUNT()、AVG()、SUM()、MIN()、MAX() 常用於統計報表，也是 BI 與經營分析最常見的基本 SQL 能力。

計算資料筆數。

計算平均值。

計算總和。

找出最小值與最大值。

SELECT COUNT(*) AS OrderCount,
       AVG(Freight) AS AvgFreight,
       MAX(Freight) AS MaxFreight
FROM Orders;

SELECT SUM(Price * Quantity) AS TotalRevenue
FROM OrderDetails;

SELECT MIN(Price) AS LowestPrice,
       MAX(Price) AS HighestPrice
FROM Products;

SELECT ShipCountry, AVG(Freight) AS AvgFreight
FROM Orders
GROUP BY ShipCountry
ORDER BY AvgFreight DESC;

觀念： 聚合函式會把多筆資料壓縮成摘要結果，因此若同時查一般欄位，通常要搭配 GROUP BY。