title: How to create database trigger to warn if some rows are not inserted yet?
body: <p>How it is technically possible to create trigger to warn if there is now rows in other table at the same time when inserting data into another table?</p>
  <p>I think BEFORE INSERT trigger does not work if there is nothing to compare at, right ?</p>
  <p>Would it be then wise to create audit table where to insert something (some ID) first, using AFTER INSERT and THEN check with trigger and warn if rows missing from other table?</p>
  <p>Could you provide some sample or easy explanation how to achieve this?
  Interests me technically more than constraint options.</p>
  <p>Thank you.</p>