服务器之家:专注于服务器技术及软件下载分享
分类导航

Mysql|Sql Server|Oracle|Redis|MongoDB|PostgreSQL|Sqlite|DB2|mariadb|Access|数据库技术|

服务器之家 - 数据库 - Mysql - SQL GROUP BY 详解及简单实例

SQL GROUP BY 详解及简单实例

2020-07-12 18:30服务器之家 Mysql

这篇文章主要介绍了SQL GROUP BY 详解及简单实例的相关资料,需要的朋友可以参考下

 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

?
1
2
3
4
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:

?
1
2
3
4
SELECT Shippers.ShipperName,COUNT(Orders.OrderID) AS NumberOfOrders FROM Orders
LEFT JOIN Shippers
ON Orders.ShipperID=Shippers.ShipperID
GROUP BY ShipperName;

GROUP BY 一个以上的列

我们也可以对一个以上的列应用 GROUP BY 语句,如下所示:

?
1
2
3
4
5
6
7
8
SELECT Shippers.ShipperName, Employees.LastName,
COUNT(Orders.OrderID) AS NumberOfOrders
FROM ((Orders
INNER JOIN Shippers
ON Orders.ShipperID=Shippers.ShipperID)
INNER JOIN Employees
ON Orders.EmployeeID=Employees.EmployeeID)
GROUP BY ShipperName,LastName;

感谢阅读,希望能帮助到大家,谢谢大家对本站的支持!

延伸 · 阅读

精彩推荐