Conceptually, an index in a database is like an index in a book. In a book, the index relates each indexed term to the page or pages on which that word appears. In a database, the index relates each indexed column value to the physical location at which the row of data containing the indexed value is stored.
A join index is a special type of index used in Sybase IQ. Join indexes may improve response time for queries that join two or more tables. In certain situations, ad hoc queries may be preferred instead of join indexes.
