use  Northwind

select CategoryName
from Categories
where CategoryID in (select CategoryID from Categories where CategoryID=1)

--AVG ES PARA SACAR PROMEDIOS  1
select ProductName,UnitPrice
from Products 
where UnitPrice>(Select AVG(UnitPrice)
from Products );
--segunda
select ContactName 
from customers 
where CustomerID in (select distinct CustomerID from Customers)

--tercera

SELECT CategoryName, AVG(Price) AS AvgPrice, Price
FROM (
SELECT p. ProductID, c. CategoryName, p.UnitPrice AS Price FROM Products P
JOIN Categories c ON p.CategoryID = c. CategoryID

) AS ProductCategory
GROUP BY CategoryName

--cuarta
select EmployeeID,
