SQL GROUP BY

Problem: List the number of products for each supplier, sorted high to low.

SELECT S.CompanyName, COUNT(P.Id) AS Products 
  FROM Supplier S
  JOIN Product P ON S.Id = P.SupplierId
 GROUP BY S.CompanyName
 ORDER BY COUNT(P.Id) DESC

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GROUP BY syntax.

SELECT column-names
  FROM table-name
 WHERE condition
 GROUP BY column-names

GROUP BY syntax with ORDER BY.

SELECT column-names
  FROM table-name
 WHERE condition
 GROUP BY column-names
 ORDER BY column-names

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SELECT Country, COUNT(Id) AS Count 
  FROM Customer
 GROUP BY Country

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SELECT Country, COUNT(Id) AS Count 
  FROM Customer
 GROUP BY Country
 ORDER BY COUNT(Id) DESC

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SELECT C.FirstName, C.LastName, SUM(O.TotalAmount) AS Total 
  FROM [Order] O 
  JOIN Customer C ON O.CustomerId = C.Id
 GROUP BY C.FirstName, C.LastName
 ORDER BY SUM(O.TotalAmount) DESC

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This query JOINs Order with Customer to obtain customer names.

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