$query = db_select('table_name', 'alias')
  ->fields('alias', array('field1', 'field2'))
  ->condition('field_name', $value, 'operator');
$result = $query->execute();

$query = db_select('node', 'n')
  ->fields('n', array('nid', 'title'))
  ->condition('type', 'article', '=');
$articles = $query->execute();

// 大于
$query->condition('created', strtotime('-1 month'), '>');

// 不等于
$query->condition('status', 0, '<>');

// LIKE操作
$query->condition('title', '%Drupal%', 'LIKE');

$query = db_select('users', 'u')
  ->fields('u', array('uid', 'name'))
  ->condition('status', 1)
  ->condition('created', strtotime('-1 year'), '>')
  ->condition('name', '%admin%', 'LIKE');

$query = db_select('node', 'n')
  ->fields('n', array('nid', 'title'));
$or = db_or()
  ->condition('type', 'article')
  ->condition('type', 'page');
$query->condition($or);

$query = db_select('node', 'n')
  ->fields('n', array('nid', 'title'))
  ->condition('changed', 'created', '>');

$types = array('article', 'page', 'blog');
$query->condition('type', $types, 'IN');

$query = db_select('node', 'n')
  ->fields('n', array('nid', 'title'))
  ->condition('type', array('forum', 'poll'), 'NOT IN');

// 获取过去一个月内发布的所有已发布文章
$query = db_select('node', 'n')
  ->fields('n', array('nid', 'title', 'created'))
  ->condition('type', 'article')
  ->condition('status', 1)
  ->condition('created', strtotime('-1 month'), '>')
  ->orderBy('created', 'DESC')
  ->range(0, 10);

$results = $query->execute();

foreach ($results as $row) {
  echo $row->title . ' (' . format_date($row->created) . ')<br>';
}