User`s guide

request. If not, it goes to the second order number, and checks that customer name. When an order
number is reached that contains the correct customer name, the database engine retrieves the
information, then continues to the next order number. Using this technique, both the Order# field and
the Customer field must be read for every single record in the table. This takes a long time and a large
amount of computer processing effort for examining extensive database tables with thousands, or even
millions of records.
Instead, you can create an index for the table based on the Customer field. Such an index might look
like this:
Pointer to Order#Customer
10444Allez Distribution
10470BG Mountain Inc.
10511BG Mountain Inc.
10501La Bomba de Bicicleta
10488Mountain Toad
10568Mountain Tops Inc.
10495SFB Inc.
10544Sierra Bicycle Group
10579Sierra Bicycle Group
10485Sierra Mountain
In this index, information is organized by customers, not order numbers. Also, notice that the second
column actually contains pointers to specific order numbers in the original table. By using this index,
the database engine can search just the information in the Customer column until it finds the customer
you are interested in, Sierra Bicycle Group.
For each correct customer entry the database engine finds in the index, it looks up the matching order
in the table according to the pointer in the second column of the index. Only the orders for the correct
customer are read. Finally, since information in the index is organized according to the customer names,
2012-03-14506
Understanding Databases