Check if a term name exists in a vocabulary

Seems silly that it's so hard to target a taxonomy term in a specific vocabulary. Here's the function I wrote to solve this problem. It's pretty flexible, but has only been tested on Drupal 6:

/**
 * Function to get Drupal taxonomy term id for a given vocabulary.  Both term and 
 * vocabulary may be passed either as a numeric id or the name as a string.  Name 
 * matches are case insensitive and strip leading and trailing spaces.
 * 
 * @param mixed $term   The ID or name of desired term
 * @param mixed $vocab  The ID or name of desired vocabulary
 * @return mixed        Returns the term ID, or NULL if term is not found
 */
function get_taxonomy_term_by_vocab( $term, $vocab ){
   $sql = "";
   
   // if both are ids 
   if(  is_numeric( $vocab ) && is_numeric( $term ) )
      $sql = "SELECT tid FROM term_data WHERE vid=$vocab AND tid=$term";
   
   // if vocab is id and term is name
   if( is_numeric( $vocab ) && !is_numeric( $term ) )
      $sql = "SELECT tid FROM term_data WHERE vid=$vocab AND TRIM(BOTH ' ' FROM `name`) LIKE '$term'";
   
   // if vocab is name and term is id
   if( !is_numeric( $vocab ) && is_numeric( $term ) ){
      $sql  = "SELECT term_data.tid FROM term_data INNER JOIN vocabulary ON term_data.vid = vocabulary.vid ";
      $sql .= "WHERE TRIM(BOTH ' ' FROM vocabulary.`name`) LIKE '$vocab' AND ";
      $sql .= "term_data.tid = $term";
   }   
   // if both are names
   if( !is_numeric( $vocab ) && !is_numeric( $term ) ){
      $sql  = "SELECT term_data.tid FROM term_data INNER JOIN vocabulary ON term_data.vid = vocabulary.vid ";
      $sql .= "WHERE TRIM(BOTH ' ' FROM vocabulary.`name`) LIKE '$vocab' AND ";
      $sql .= "TRIM(BOTH ' ' FROM term_data.`name`) LIKE '$term'";
   }
   
   // do query
   $tid_rsrc = db_query($sql);
   $row = db_fetch_array($tid_rsrc, MYSQL_ASSOC);
   return $row['tid'];   
}