MySQL GROUP BY

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MySQL GROUP BY 语句

GROUP BY 语句将具有相同值的行分组为汇总行，例如"查找每个地区的客户数量"。

GROUP BY 语句通常与聚合函数（COUNT()、MAX(), MIN(), SUM(), AVG()) 按一列或多列对结果集进行分组。

GROUP BY 语法

SELECT column_name(s)
FROM table_name
WHERE condition
GROUP BY column_name(s)
ORDER BY column_name(s);

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演示数据库

以下是 Northwind 示例数据库中"Customers"表的选择:

CustomerID	CustomerName	ContactName	Address	City	PostalCode	Country
1	Alfreds Futterkiste	Maria Anders	Obere Str. 57	Berlin	12209	Germany
2	Ana Trujillo Emparedados y helados	Ana Trujillo	Avda. de la Constitución 2222	México D.F.	05021	Mexico
3	Antonio Moreno Taquería	Antonio Moreno	Mataderos 2312	México D.F.	05023	Mexico
4	Around the Horn	Thomas Hardy	120 Hanover Sq.	London	WA1 1DP	UK
5	Berglunds snabbköp	Christina Berglund	Berguvsvägen 8	Luleå	S-958 22	Sweden

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MySQL GROUP BY 示例

下面的 SQL 语句列出了每个地区的客户数量:

实例

SELECT COUNT(CustomerID), Country
FROM Customers
GROUP BY Country; 亲自试一试 »

下面的 SQL 语句列出了每个地区的客户数量，从高到低排序:

实例

SELECT COUNT(CustomerID), Country
FROM Customers
GROUP BY Country
ORDER BY COUNT(CustomerID) DESC; 亲自试一试 »

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演示数据库

以下是 Northwind 示例数据库中"Orders"表的选择:

OrderID	CustomerID	EmployeeID	OrderDate	ShipperID
10248	90	5	1996-07-04	3
10249	81	6	1996-07-05	1
10250	34	4	1996-07-08	2

以及从"Shippers"表中选择的内容:

ShipperID	ShipperName
1	Speedy Express
2	United Package
3	Federal Shipping

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GROUP BY 与 JOIN 示例

以下SQL语句列出了每个发货人发送的订单数量:

实例

SELECT Shippers.ShipperName, COUNT(Orders.OrderID) AS NumberOfOrders FROM Orders
LEFT JOIN Shippers ON Orders.ShipperID = Shippers.ShipperID
GROUP BY ShipperName; 亲自试一试 »

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学习训练

测验:

列出每个地区的客户数量。

SELECT (CustomerID),
Country
FROM Customers
;

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