GROUP BY 语句将具有相同值的行分组为汇总行，例如“查找每个国家/地区的客户数量”。
GROUP BY 语句通常与聚合函数（COUNT()、MAX()、MIN()、SUM()、AVG()）一起使用，以按一列或多列对结果集进行分组。
SELECT column_name(s)
FROM table_name
WHERE condition
GROUP BY column_name(s)
ORDER BY column_name(s)
以下是“Northwind”数据库的“Customers”（“Customers”）表中的示例：
| 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. | 5021 | Mexico |
| 3 | Antonio Moreno Taquería | Antonio Moreno | Mataderos 2312 | México D.F. | 5023 | 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 |
以下 SQL 语句列出了每个国家/地区的客户数量：
Run SQLSELECT COUNT(CustomerID), Country
FROM Customers
GROUP BY Country
以下 SQL 语句列出了每个国家/地区的客户，按从高到低排序：
Run SQLSELECT COUNT(CustomerID), Country
FROM Customers
GROUP BY Country
ORDER BY COUNT(CustomerID) DESC
以下是“Northwind”数据库的“Orders”（“Orders”）表中的示例：
| ProductID | OrderID | CustomerID | EmployeeID | OrderDate | ShipperID |
|---|---|---|---|---|---|
| 1 | 10248 | 90 | 5 | 1996-07-04 | 3 |
| 2 | 10249 | 81 | 6 | 1996-07-05 | 1 |
| 3 | 10250 | 34 | 4 | 1996-07-08 | 2 |
| 4 | 10251 | 84 | 3 | 1996-07-08 | 1 |
| 5 | 10252 | 76 | 4 | 1996-07-09 | 2 |
以及表“Shippers”（“发件人”）中的示例：
| ShipperID | ShipperName | Phone |
|---|---|---|
| 1 | Speedy Express | (503) 555-9831 |
| 2 | United Package | (503) 555-3199 |
| 3 | Federal Shipping | (503) 555-9931 |
下面的SQL语句列出了每个发送者发送的订单数量：
Run SQLSELECT Shippers.ShipperName, COUNT(Orders.OrderID) AS NumberOfOrders
FROM Orders
LEFT JOIN Shippers
ON Orders.ShipperID = Shippers.ShipperID
GROUP BY ShipperName