title: Is a descending index beneficial for SELECT..WHERE in the case when the value being located is near the maximum in the table?
body: <p>Using: Firebird 2.5.3</p>
  
  <p>This is something that I couldn't ascertain from the (current) Firebird docs regarding table indexes.</p>
  
  <p>Table structure is like so: </p>
  
  <pre><code>CREATE TABLE CHILDTABLE 
  (
    ROW_ID                  INTEGER         NOT NULL,
    PARENT_ID                 INTEGER         NOT NULL,
   CONSTRAINT PK_CHILDTABLE  PRIMARY KEY (ROW_ID)
  );
  </code></pre>
  
  <p>A query that will select 1 or more rows from this table looks like this:</p>
  
  <pre><code>SELECT ROW_ID FROM CHILDTABLE WHERE PARENT_ID = ?
  </code></pre>
  
  <p>Questions: </p>
  
  <ol>
  <li><p>Given that every time this query is sent to the database, it will ask for a PARENT_ID value (the parameter) which is near the maximum of the set of values in the table (and also among its most recently added rows), will a descending index be preferred over an ascending one, for the purpose of retrieving the result quicker/faster from the database?</p></li>
  <li><p>Given the scenario, is there any negative performance impact to use the descending index instead of an ascending index? (Eg. Would more processing need to be done by the server for every row inserted if it were a descending index instead of an ascending index, and how will indexes affect insert performance on the table as it grows in size?)</p></li>
  </ol>