Beginning SQL

Chapter 3
The results are as follows:
City MemberId
Big City 8
New Town 4
Orange Town 5
Orange Town 6
Orange Town 7
Townsville 1
Windy Village 9
Orange Town appears three times because MemberId is unique on each row. In fact, using the DISTINCT
keyword where one of the columns is always unique is pointless.
Using Aliases
Just as James Bond is also known by the alias 007, you can give column names an alias in the results. An
alias is simply a secondary or symbolic name for a collection of data. If, for example, instead of
LastName you want your results to return an alias called Surname, you would write the following
query:
SELECT LastName AS Surname FROM MemberDetails;
Specifying Surname with the AS keyword tells the database system that you want the results to be
known as the alias Surname. Using an alias doesn’t change the results returned in any way, nor does it
rename the LastName in the MemberDetails tables. It affects only the name of the column in the results
set. Using aliases may not seem that useful right now, but later on in the book you use aliases as a shorthand
way of referring to table names, among other uses.
So far all the data from tables has been returned, but what if you just want specific data — for example,
details of members older than 60 years old? In such a case, you need to use a WHERE clause, which is the
topic of the next section.
Filtering Results with the WHERE Clause
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Although you may occasionally have to select all the records in a table, it’s much more common to filter
results so that you get only the information you want. For example, you could filter query results to find
out all the names of members living in New State. In Chapter 2 you saw how you can use the WHERE
clause to update or delete specific records. You can also use the WHERE clause with SELECT statements to
filter results so that you get back only the data you want.