There is no need to use IF EXISTS() with db_query(). Drupal core code never use it.
// comment_num_new()
return db_query('SELECT COUNT(cid) FROM {comment} WHERE nid = :nid AND created > :timestamp AND status = :status', array(
':nid' => $nid,
':timestamp' => $timestamp,
':status' => COMMENT_PUBLISHED,
))->fetchField();
// aggregrator_cron()
$result = db_query('SELECT * FROM {aggregator_feed} WHERE queued = 0 AND checked + refresh < :time AND refresh <> :never', array(
':time' => REQUEST_TIME,
':never' => AGGREGATOR_CLEAR_NEVER,
));
$queue = DrupalQueue::get('aggregator_feeds');
foreach ($result as $feed) {
if ($queue->createItem($feed)) {
// Add timestamp to avoid queueing item more than once.
db_update('aggregator_feed')->fields(array('queued' => REQUEST_TIME))->condition('fid', $feed->fid)->execute();
}
}
// aggregrator_feed_load()
$feeds = &drupal_static(__FUNCTION__);
if (!isset($feeds[$fid])) {
$feeds[$fid] = db_query('SELECT * FROM {aggregator_feed} WHERE fid = :fid', array(':fid' => $fid))->fetchObject();
}
return $feeds[$fid];
// aggregrator_expire()
$iids = db_query('SELECT iid FROM {aggregator_item} WHERE fid = :fid AND timestamp < :timestamp', array(
':fid' => $feed->fid,
':timestamp' => $age,
))->fetchCol();
if ($iids) {
db_delete('aggregator_category_item')->condition('iid', $iids, 'IN')->execute();
db_delete('aggregator_item')->condition('iid', $iids, 'IN')->execute();
}
In your case, the following code is enough.
if ($nid = db_query("SELECT nid FROM {node} WHERE type = :type1 AND uid = '123'", array("type1" => 'nodetype_x'))->fetchField()) {
// There is such a node.
}
else {
// There isn't such a node.
}