An Index can improve the performance of queries that select a small percentage of rows from a table. A general guideline is to create indexes on tables that are queried for less than 2% - 4% of the table's rows, with the following assumptions:
-
Rows with the same value for the column on which the query is based are uniformly distributed throughout the data blocks allocated to the table
-
Rows in the table are randomly ordered with respect to the column on which the query is based
-
Each data block allocated to the table contains at least 10 rows
-
The table contains a relatively small number of columns
-
Most queries on the table have relatively simple WHERE clauses
|
