A database term.

An index is a list that provides the location of the items within the database. For example most text books (which are a kind of paper database) have an index at the back where key words or sections are listed by page number.

In a database, an index of records based on the primary key is created by the system. Records are then found by querying the index. There can also be secondary indexes that locate records in a different order to the primary method. For example a simple record might be

UserID Names City Postcode
110 David Jones Coventry CV4 2NT
120 Arthur Morgan Exeter EX3 8TH

In this case the primary key index locates records based on UserID and a secondary index might locate records by City.

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