Check if a value exist i a query

[eluser]Quaotloa[/eluser]
Hi, I have been using this code in "traditional PHP".

$query = SELECT groupid FROM user_group WHERE groupid NOT IN(".
"SELECT groupid FROM user_group WHERE userid = $userID)

$array = mysql_fetch_query($query),

When i want to store values NOT IN the second query...


But when i use this query inside a codeingiter model or controller, i get this error message

Severity: Warning

Message: mysql_fetch_array(): supplied argument is not a valid MySQL result resource


How can i fix it? Can it be done by active records?

Regards
Fredrik