title: SQL INSERT from HTML Input with checking for already existing
body: <p>With a HTML/php Webinterface i am putting some variables to a mysql datebase.
  The query works fine like this:</p>
  <p><code>INSERT INTO &quot;. $tabledb_stack .&quot; (ANr, Operator) VALUES ('&quot;. $ANr .&quot;', '&quot;. $Operator .&quot;')  </code></p>
  <p>But now i need to check if the ANr Value is already in the database.
  But just the ANr number and no other Value. Then it should not write it into the database.
  I tried with a WHERE NOT EXISTS statement, but it isnt working.</p>
  <p>Any hints how i can try it?</p>
  <p>Thx</p>