根据分类得到节点

从 taxonomy 模块里面找 
12行左右function taxonomy_term_page($
46行左右$output = theme('taxonomy_term_page', $tids, taxonomy_select_nodes($tids, $terms['operator'], $depth, TRUE));

function taxonomy_select_nodes($tids = array(), $operator = 'or', $depth = 0, $pager = TRUE, $order = 'n.sticky DESC, n.created DESC') {
  if (count($tids) > 0) {
    // For each term ID, generate an array of descendant term IDs to the right depth.
    $descendant_tids = array();
    if ($depth === 'all') {
      $depth = NULL;
    }
    foreach ($tids as $index => $tid) {
      $term = taxonomy_get_term($tid);
      $tree = taxonomy_get_tree($term->vid, $tid, -1, $depth);
      $descendant_tids[] = array_merge(array($tid), array_map('_taxonomy_get_tid_from_term', $tree));
    }

    if ($operator == 'or') {
      $args = call_user_func_array('array_merge', $descendant_tids);
      $placeholders = db_placeholders($args, 'int');
      $sql = 'SELECT DISTINCT(n.nid), n.sticky, n.title, n.created FROM {node} n INNER JOIN {term_node} tn ON n.vid = tn.vid WHERE tn.tid IN (' . $placeholders . ') AND n.status = 1 ORDER BY ' . $order;
      $sql_count = 'SELECT COUNT(DISTINCT(n.nid)) FROM {node} n INNER JOIN {term_node} tn ON n.vid = tn.vid WHERE tn.tid IN (' . $placeholders . ') AND n.status = 1';
    }
    else {
      $joins = '';
      $wheres = '';
      $args = array();
      foreach ($descendant_tids as $index => $tids) {
        $joins .= ' INNER JOIN {term_node} tn' . $index . ' ON n.vid = tn' . $index . '.vid';
        $wheres .= ' AND tn' . $index . '.tid IN (' . db_placeholders($tids, 'int') . ')';
        $args = array_merge($args, $tids);
      }
      $sql = 'SELECT DISTINCT(n.nid), n.sticky, n.title, n.created FROM {node} n ' . $joins . ' WHERE n.status = 1 ' . $wheres . ' ORDER BY ' . $order;
      $sql_count = 'SELECT COUNT(DISTINCT(n.nid)) FROM {node} n ' . $joins . ' WHERE n.status = 1 ' . $wheres;
    }
    $sql = db_rewrite_sql($sql);
    $sql_count = db_rewrite_sql($sql_count);
    if ($pager) {
      $result = pager_query($sql, variable_get('default_nodes_main', 10), 0, $sql_count, $args);
    }
    else {
      $result = db_query_range($sql, $args, 0, variable_get('feed_default_items', 10));
    }
  }

  return $result;
}

来自 https://api.drupal.org/api/drupal/modules!taxonomy!taxonomy.module/function/taxonomy_select_nodes/6