Question

Today, I came across a query on W3Schools here : http://www.w3schools.com/sql/sql_view.asp which was written as below:

CREATE VIEW [Category Sales For 1997] AS
SELECT DISTINCT CategoryName,Sum(ProductSales) AS CategorySales
FROM [Product Sales for 1997]
GROUP BY CategoryName

I am wondering what’s the purpose of using DISTINCT in this query? The query has already GROUPed BY the result set, so there is no chances of same CategoryName after doing GROUP BY and before doing SELECT. Would this query behave differently if it did not use DISTINCT? I mean what would happen if it was written simply as this:

CREATE VIEW [Category Sales For 1997] AS
SELECT CategoryName,Sum(ProductSales) AS CategorySales
FROM [Product Sales for 1997]
GROUP BY CategoryName

Thank you!

Answer 1

You can remove it. It’s redundant and has no effect on the output.