Index use and access paths

Index use and access paths If you define an index on a column or columns, the query optimizer can use the index to find data in the column more quickly.

automatically creates indexes to back up primary key, foreign key, and unique constraints, so those indexes are always available to the optimizer, as well as those that you explicitly create with the CREATE INDEX command. The way gets to the data -- through an index or directly through the table -- is called the access path.