title: Does Oracle automatically create a secondary index for FOREIGN KEY columns?
body: <p>I'm currenly developing on Oracle. I have several tables for which I defined FOREIGN KEY constraints. I have already read this <a href="https://stackoverflow.com/questions/836167/does-a-foreign-key-automatically-create-an-index">SQL Server</a>-oriented and this <a href="https://stackoverflow.com/questions/304317/does-mysql-index-foreign-key-columns-automatically">MySQL</a>-oriented questions but I could find none about Oracle.</p>
  
  <p>So the question is always the same: in order to optimize query performance, for those columns for which I create a FOREIGN KEY constraint, do I also have to create an explicit secondary index? Doesn't Oracle automatically create an index on FOREIGN KEYed columns to boost performances during JOINs?</p>
  
  <p>I usually perform queries in which the WHERE clause compare against those columns.</p>