SQL GROUP BY

Unique SQL归档

2015-09-07 0 931

SQL GROUP BY 语句

Aggregate 函数常常需要添加 GROUP BY 语句。

GROUP BY 语句

GROUP BY 语句用于结合 Aggregate 函数，根据一个或多个列对结果集进行分组。

SQL GROUP BY 语法

SELECT column_name, aggregate_function(column_name)
FROM table_name
WHERE column_name operator value
GROUP BY column_name;

演示数据库

在本教程中，我们将使用众所周知的 Northwind 样本数据库。

下面是选自 ”Orders” 表的数据：

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

选自 ”Shippers” 表的数据：

ShipperID	ShipperName	Phone
1	Speedy Express	(503) 555-9831
2	United Package	(503) 555-3199
3	Federal Shipping	(503) 555-9931

选自 ”Employees” 表的数据：

EmployeeID	LastName	FirstName	BirthDate	Photo	Notes
1	Davolio	Nancy	1968-12-08	EmpID1.pic	Education includes a BA….
2	Fuller	Andrew	1952-02-19	EmpID2.pic	Andrew received his BTS….
3	Leverling	Janet	1963-08-30	EmpID3.pic	Janet has a BS degree….

SQL GROUP BY 实例

现在我们想要查找每个送货员配送的订单数目。

下面的 SQL 语句按送货员进行订单分类统计：

实例

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

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