Multiple WHERE functions in SQL - sql

Question

I'm trying to write an SQL query to return information including product code, yearly sales revenues, costs, sales people information from two different tables. I need to return the product ID information for the product with the lowest'onboarding cost' for the 'north' region.
I have used WHERE Region = 'North' to just get the product info for the North region, and ORDER BY onboarding cost; to sort this low to high and find the product with the lowest cost. Is there a way of just returning the product with the lowest onboarding cost for the north region?

Answer 1

In the WHERE clause you could add:
... AND onboarding cost=(SELECT MAX(onboarding cost) FROM ... WHERE region='North' ...)
SELECT
ProductRevenueAndCosts.ProductID,
ProductRevenueAndCosts.SalesRevenueYear1,
ProductRevenueAndCosts.SalesRevenueYear2,
ProductRevenueAndCosts.OperationalCostsYear1,
ProductRevenueAndCosts.OperationalCostsYear2,
ProductRevenueAndCosts.OnboardingCost,
SalesPeople.FirstName,
SalesPeople.LastName,
SalesPeople.Region
FROM SalesPeople INNER JOIN ProductRevenueAndCosts ON
SalesPeople.SalesPersonID = ProductRevenueAndCosts.SalesPersonID
WHERE SalesPeople.Region = "North"
AND ProductRevenueAndCosts.OnboardingCost=(
SELECT MAX(ProductRevenueAndCosts.OnboardingCost)
FROM SalesPeople INNER JOIN ProductRevenueAndCosts ON
SalesPeople.SalesPersonID = ProductRevenueAndCosts.SalesPersonID
WHERE SalesPeople.Region = "North"
)
ORDER BY ProductRevenueAndCosts.Onboardingcost DESC -- this is obsolete
;
But this will eventually return more than one result - in case that more than one product has the same highest onboaring cost.

Answer 2

Yes, you need to limit the number of records, like this:
MySQL, PostgreSQL
SELECT
ProductRevenueAndCosts.ProductID,
ProductRevenueAndCosts.SalesRevenueYear1,
ProductRevenueAndCosts.SalesRevenueYear2,
ProductRevenueAndCosts.OperationalCostsYear1,
ProductRevenueAndCosts.OperationalCostsYear2,
ProductRevenueAndCosts.OnboardingCost,
SalesPeople.FirstName,
SalesPeople.LastName,
SalesPeople.Region
FROM SalesPeople INNER JOIN ProductRevenueAndCosts ON
SalesPeople.SalesPersonID = ProductRevenueAndCosts.SalesPersonID
WHERE SalesPeople.Region = "North"
ORDER BY ProductRevenueAndCosts.Onboardingcost DESC
LIMIT 0, 1;
Where 0 is the starting index (first row) and 1 is the number of records you want to get.
SQL Server
SELECT TOP 1
ProductRevenueAndCosts.ProductID,
ProductRevenueAndCosts.SalesRevenueYear1,
ProductRevenueAndCosts.SalesRevenueYear2,
ProductRevenueAndCosts.OperationalCostsYear1,
ProductRevenueAndCosts.OperationalCostsYear2,
ProductRevenueAndCosts.OnboardingCost,
SalesPeople.FirstName,
SalesPeople.LastName,
SalesPeople.Region
FROM SalesPeople INNER JOIN ProductRevenueAndCosts ON
SalesPeople.SalesPersonID = ProductRevenueAndCosts.SalesPersonID
WHERE SalesPeople.Region = "North"
ORDER BY ProductRevenueAndCosts.Onboardingcost DESC;
Where TOP 1 tells the RDBMS that you are interested only in the very first row.
Oracle
SELECT
ProductRevenueAndCosts.ProductID,
ProductRevenueAndCosts.SalesRevenueYear1,
ProductRevenueAndCosts.SalesRevenueYear2,
ProductRevenueAndCosts.OperationalCostsYear1,
ProductRevenueAndCosts.OperationalCostsYear2,
ProductRevenueAndCosts.OnboardingCost,
SalesPeople.FirstName,
SalesPeople.LastName,
SalesPeople.Region
FROM SalesPeople INNER JOIN ProductRevenueAndCosts ON
SalesPeople.SalesPersonID = ProductRevenueAndCosts.SalesPersonID
WHERE SalesPeople.Region = "North"
ORDER BY ProductRevenueAndCosts.Onboardingcost DESC
OFFSET 0 ROWS FETCH NEXT 1 ROWS ONLY;