// Drupal 6
$value = db_query("SELECT nid FROM {node} WHERE uid = %d AND type = '%s'", 5, 'page');
 
// Drupal 7
$value = db_query("SELECT nid FROM {node} WHERE uid = :uid AND type = :type", array(
  ':uid' => 5,
  ':type' => 'page',
))->fetchField();

// Drupal 6
$result = db_query("SELECT * FROM {table}");
while ($row = db_fetch_object($result)) { /* ... */ }
 
// Drupal 7
$result = db_query("SELECT * FROM {table}");
foreach ($result as $row) { /* ... */ }

// Drupal 6
db_query("UPDATE {node} SET title='%s', status=%d WHERE uid=%d", 'hello world', 1, 5);
 
// Drupal 7
db_update('node')->fields(array('title' => 'hello world', 'status' => 1))->condition('uid', 5)->execute();

// Drupal 6
db_query("DELETE FROM {node} WHERE uid=%d AND created < %d", 5, time() - 3600);
 
// Drupal 7
db_delete('node')->condition('uid', 5)->condition('created', time() - 3600, '<')->execute();

// Drupal 6
db_query("INSERT INTO {mytable} (intvar, stringvar, floatvar) VALUES (%d, '%s', %f)", 5, 'hello world', 3.14);
$id = db_last_insert_id();
 
// Drupal 7
$id = db_insert('mytable')->fields(array(
    'intvar' => 5,
    'stringvar' => 'hello world',
    'floatvar' => 3.14,
))->execute();