Title: Describe issues that affect the decision to create an index.
Course: Database Design and Management (Oracle) (10052) > Section: Creating Additional Database Objects

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