# CTE Resource Center - Verso - Database Design and Management (Oracle) Task 1955277945

CTE Resource Center - Verso

Virginia’s CTE Resource Center

Describe issues that affect the decision to create an index.

Definition

Description should include the following questions and issues that can affect the runtime speed of the query:
  • Does the column have a wide range of values?
  • Does the column contain a large number of nulls?
  • Are columns used frequently in a WHERE?
  • Is the table large and are most queries designed to retrieve 2 percent to 4 percent of rows?
When the following are true, an index should be created:
  • When the column is used frequently in a WHERE clause or a join condition
  • When the column contains a wide range of values
  • When the column contains a large number of null values
  • When two or more columns are frequently used together in a WHERE clause or a join condition
  • When the table is large and most queries are expected to retrieve less than 2 percent to 4 percent of the rows
When the following are not true, an index should not be created:
  • When the table is small
  • When the columns are not often used as a condition in the query
  • When most queries are expected to retrieve more than 2 percent to 4 percent of the rows.
  • When the table is updated frequently