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SQL GROUP BY 语句


SQL GROUP BY 语句

GROUP BY语句将具有相同值的行分组到汇总行中,例如“查找每个国家的客户数”。

GROUP BY语句通常与聚合函数(COUNT,MAX,MIN,SUM,AVG)一起使用,将结果集分组为一列或多列。

GROUP BY语法

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

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 Constituciуn 2222 Mйxico D.F. 05021 Mexico
3 Antonio Moreno Taquerнa Antonio Moreno Mataderos 2312 Mйxico D.F. 05023 Mexico
4 Around the Horn Thomas Hardy 120 Hanover Sq. London WA1 1DP UK
5 Berglunds snabbkцp Christina Berglund Berguvsvдgen 8 Luleе S-958 22 Sweden

SQL GROUP BY 实例

以下SQL语句列出了每个国家的客户数量:

实例

SELECT COUNT(CustomerID), Country
FROM Customers
GROUP BY Country;

亲自尝试»

以下SQL语句列出了每个国家的客户数量,从高到低排序:

实例

SELECT COUNT(CustomerID), Country
FROM Customers
GROUP BY Country
ORDER BY COUNT(CustomerID) DESC;

亲自尝试»


演示数据库

以下是Northwind实例数据库中“Orders”表查询:

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

并从“Shippers”表中查询:

ShipperID ShipperName
1 Speedy Express
2 United Package
3 Federal Shipping

GROUP BY 和 JOIN 实例

以下SQL语句列出了每个出货单发送的订单数:

实例

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

亲自尝试»