title: "Insert if not exists" in both MySQL and HSQLDB
body: <p>Is there a SQL statement (or atomic sequence of statements) supported by both MySQL and HSQLDB to insert values if they aren't already there?</p>
  
  <p>I'm working on an app that uses MySQL as its production database and HSQLDB for unit tests; I'd like to have a single "initial data import when the tables are empty" script.</p>
  
  <p>MySQL supports <code>INSERT IGNORE</code>, <code>REPLACE INTO</code> and <code>INSERT INTO ... ON DUPLICATE KEY UPDATE ...</code>, but HSQLDB doesn't; conversely, HSQLDB supports <code>MERGE</code> but MySQL doesn't.</p>