Sql Query using group clause

Question

this is my table snapshot of sql server.

i want to write a sql query , which will return only 3 row, whcih contain max offer from 3 diffrent category. like in my result there should be 3 different category id, and correspondence to that category's Offer that offer should be maximum in that category

this is my desired output

as you can see there is 3 diffrent category , and offer belongs to that category is maximum from that category

see

Answer 1

There 2 different approach to your query:

select * from (
select *, dense_rank() over( order by ct desc) t from (
select *, max(Offer) over (partition by cat_id) ct from Products
) o)o2 where t<3

or

select * from Products s inner join (
select top 3 Cat_id, max(Offer) max_offer from Products
group by Cat_id
order by max_offer desc) o on o.Cat_id=s.Cat_id

Answer 2

If you just want the Category and the maximum value:

SELECT TOP 3 Cat_Id, MAX(Offer) FROM Products GROUP BY Cat_Id

But if you want also other fields, you have to use a rank function:

SELECT TOP 3 * FROM
    (SELECT ROW_NUMBER() OVER(PARTITION BY Cat_Id ORDER BY Offer DESC) AS RowNumber,
        Cat_Id, Offer, Name, Model
     FROM Products) AS T
WHERE RowNumber=1