title: Firebird " Column does not belong to referenced table "
body: <p>I am trying to create my first procedure on firebird 2.5 by using ibexpert gui. </p>
  
  <p>The procedure will return 'PROCESS_DATE' which belongs to a specific 'PROCESS_ID'. I prepared following code:</p>
  
  <pre><code>begin
    OUTPUT_DATE = (select PROCESS_DATE from PROCESSES
                   where PROCESS_ID = INPUT_ID);
    suspend;
  end
  </code></pre>
  
  <p>input parameter  : 'INPUT_ID' --> type 'INTEGER'<br>
  output parameter : 'OUTPUT_DATE' --> type 'DATE'</p>
  
  <p>But when I tried to compile it returns this error:</p>
  
  <pre><code>Column does not belong to referenced table.
  Dynamic SQL Error.
  SQL error code = -206.
  Column unknown.
  INPUT_ID.
  At line 9, column 48.
  </code></pre>
  
  <p>I do not know how to deal with this error.</p>
  
  <p>I tried to find solutions on other questions also the internet but i couldn't find a basic, understandable answer for beginners. thanks for helps.</p>