DISTINCT and Eliminating Duplicates
Let's say that you want to list the ID and names of only those people who have sold an antique. Obviously, you want a list where each seller is only listed once -- you don't want to know how many antiques a person sold, just the fact that this person sold one (for counts, see the Aggregate Function section below). This means that you will need to tell SQL to eliminate duplicate sales rows, and just list each person only once. To do this, use the DISTINCT keyword.
First, we will need an equijoin to the AntiqueOwners table to get the detail data of the person's LastName and FirstName. However, keep in mind that since the SellerID column in the Antiques table is a foreign key to the AntiqueOwners table, a seller will only be listed if there is a row in the AntiqueOwners table listing the ID and names. We also want to eliminate multiple occurrences of the SellerID in our listing, so we use DISTINCT on the column where the repeats may occur (however, it is generally not necessary to strictly put the Distinct in front of the column name).
