The GROUP BY
statement groups rows that have the same values into summary
rows, like "find the number of customers in each country".
The GROUP BY
statement is often used with aggregate functions (COUNT()
,
MAX()
,
MIN()
, SUM()
,
AVG()
) to group the result-set by one or more columns.
SELECT column_name(s)
FROM table_name
WHERE condition
GROUP BY column_name(s)
ORDER BY column_name(s);
The following SQL statement lists the number of customers in each country:
SELECT COUNT(CustomerID), Country
FROM Customers
GROUP BY Country;
The following SQL statement lists the number of customers in each country, sorted high to low:
SELECT COUNT(CustomerID), Country
FROM Customers
GROUP BY Country
ORDER BY COUNT(CustomerID) DESC;
The following SQL statement lists the number of orders sent by each shipper:
SELECT Shippers.ShipperName, COUNT(Orders.OrderID) AS NumberOfOrders FROM
Orders
LEFT JOIN Shippers ON Orders.ShipperID = Shippers.ShipperID
GROUP BY ShipperName;