About indexes
An index helps database to find and sort records faster. When you create
a database and tune it for performance, you should create indexes for
the columns used in queries to find data.
Indexes in databases are similar to indexes in books. In a book, an
index allows you to find information quickly without reading the entire
book. In a database, an index allows the database program to find data
in a table without scanning the entire table.
You can create indexes based on a single field or on multiple fields.
Multiple-field indexes enable you to distinguish between records in which
the first field may have the same value.
The performance benefits of indexes do come with a cost. Tables with
indexes require more storage space in the database. The commands that
insert, update, or delete data can take longer and require more processing
time. You should ensure that the performance benefits outweigh the extra
cost.
Which fields to index?
You'll probably want to index fields you search frequently, fields you
sort, or fields that you join to fields in other tables in queries. The
primary key of a table is automatically indexed, and you can't index a
field whose data type is OLE Object. If many of the values in the field
are the same, the index may not significantly speed up queries. For other
fields, you should consider indexing a field if the following apply:
• The
field's data type is Text, Number, Date/Time, or Currency.
• You
anticipate searching for values stored in the field.
• You
anticipate sorting values in the field.
• You
anticipate storing many different values in the field.
Related Topics:
 How to create an
index
About Indexes Manager
Create and change indexes
About primary keys
Set or change the primary
key
Columns
About tables
Relationships
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