MySQL COUNT(), AVG() 和 SUM() 函式

The COUNT() function returns the number of rows that matches a specified criterion. (COUNT() 函式返回匹配指定條件的行數。)

COUNT() 語法

SELECT COUNT(column_name)
FROM table_name
WHERE condition;

The AVG() function returns the average value of a numeric column.

AVG() 語法

SELECT AVG(column_name)
FROM table_name
WHERE condition;

The SUM() function returns the total sum of a numeric column.

SUM() 語法

SELECT SUM(column_name)
FROM table_name
WHERE condition;

演示資料庫

Below is a selection from the "Products" table in the Northwind sample database (以下是 Northwind 示例資料庫中的 "Products" 表的選擇結果)

ProductID	ProductName	SupplierID	CategoryID	Unit	Price
1	Chais	1	1	10 boxes x 20 bags	18
2	Chang	1	1	24 - 12 oz bottles	19
3	Aniseed Syrup	1	2	12 - 550 ml bottles	10
4	Chef Anton's Cajun Seasoning	2	2	48 - 6 oz jars	22
5	Chef Anton's Gumbo Mix	2	2	36 boxes	21.35

COUNT() 示例

The following SQL statement finds the number of products

示例

SELECT COUNT(ProductID)
FROM Products;

自己動手試一試 »

注意： NULL 值不被計算。

AVG() 示例

The following SQL statement finds the average price of all products

示例

SELECT AVG(Price)
FROM Products;

自己動手試一試 »

注意： NULL 值將被忽略。

演示資料庫

Below is a selection from the "OrderDetails" table in the Northwind sample database (以下是 Northwind 示例資料庫中的 "OrderDetails" 表的選擇結果)

OrderDetailID	OrderID	ProductID	Quantity
1	10248	11	12
2	10248	42	10
3	10248	72	5
4	10249	14	9
5	10249	51	40

SUM() 示例

The following SQL statement finds the sum of the "Quantity" fields in the "OrderDetails" table

示例

SELECT SUM(Quantity)
FROM OrderDetails;

自己動手試一試 »

注意： NULL 值將被忽略。

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MySQL COUNT(), AVG() 和 SUM() 函式