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Improving performance by indexing data
Improving performance by indexing data
If you went to a bookshop to find a book and started searching
the bookshelves as you walked in, beginning with the first shelf,
it would take a long time to find the book you wanted. Books
in a shop are grouped together, often by topic, to make this
task easier. This is the idea behind an index—you can find the
book quicker by looking only at the shelves in a specific group.
Indexes speed up data retrieval.
Access will automatically add indexes to your foreign key fields
when you create relationships. You can add other indexes
manually to improve the speed of retrieving data, but this also
introduces a slight overhead when updating data. This is because
editing the data can change the indexed value (which Access
needs to maintain). Indexes work best on fields containing many
different values.
Create an index
1 In the table design view, locate the field name you want to index.
2 In the Field Properties section, select an Index allowing duplicates.
3 You can display and manage all indexes in a table by using the
Indexes popup window.
TIP Don’t bother indexing tables with less than several
thousand entries. Don’t index fields that have few distinct
values—for example, a Yes/No field. Don’t index foreign keys; Access
will do that for you. Indexes are best added when a query or report is
slow, and after adding the index, you can check to verify that the query
is faster as a result of having added the index.
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