Beginning SQL

Returning Only Distinct Rows
If you want to know all the unique values in a record, how would you go about retrieving them? The
answer is by using the DISTINCT keyword. The DISTINCT keyword is added to the SELECT statement’s
column listing, directly after the SELECT keyword. For example, if someone asks you which cities members
come from, you could try a query similar to the following:
SELECT City FROM MemberDetails;
Executing the query gives you the following results:
City
Townsville
Orange Town
New Town
Orange Town
Orange Town
Big City
Windy Village
As you can see, Orange Town is listed three times because there are three members from that city. But if
you simply want a list of the unique places that members live in, you could add the DISTINCT keyword:
SELECT DISTINCT City FROM MemberDetails;
Executing the modified query gives these results:
City
Big City
New Town
Orange Town
Townsville
Windy Village
This time, Orange Town is mentioned just once. The DISTINCT keyword works on all columns in combination;
all the columns listed in the SELECT statement must be unique. If you change the previous query
to include MemberId, which is unique for every single row, and rerun the query, you end up with all
the rows:
SELECT DISTINCT City, MemberId FROM MemberDetails;
Extracting Information
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