php - 如何在 Zend\Db\Sql 中使用聚合函数？

Question

下面的代码给出了 Zend\Db\Sql\Expression 类的错误 Object 不能被转换为字符串；

$select->join(array('tt' => 'discuss_thread_tag'),
                  'tt.tag_id = discuss_tag.tag_id',
                  array(),
                  'left')
           ->join(array('t' => 'discuss_thread'),
                  't.thread_id = tt.thread_id',
                  array(new Expression('COUNT(thread_id) AS thread_count')),
                  'left')
           ->join(array('m' => 'discuss_message'),
                  'm.thread_id = t.thread_id',
                  array(new Expression('MAX(post_time) AS last_post')),
                  //'*',
                  'left')
           ->group(array('discuss_tag.name', 'discuss_tag.slug', 'discuss_tag.description'));

我做错了什么？

Answer 1

我没有对此进行测试，但我认为它应该是这样的：

$select->join(array('tt' => 'discuss_thread_tag'),
                      'tt.tag_id = discuss_tag.tag_id',
                      array(),
                      \Zend\Db\Sql\Sql::JOIN_LEFT)
               ->join(array('t' => 'discuss_thread'),
                      't.thread_id = tt.thread_id',
                      array('thread_count' => new Expression('COUNT(thread_id)')),
                      \Zend\Db\Sql\Sql::JOIN_LEFT)
               ->join(array('m' => 'discuss_message'),
                      'm.thread_id = t.thread_id',
                      array('last_post' => new Expression('MAX(post_time)')),
                      \Zend\Db\Sql\Sql::JOIN_LEFT)
               ->group(array('discuss_tag.name', 'discuss_tag.slug', 'discuss_tag.description'));

    // Debug query
    $sql = new \Zend\Db\Sql\Sql();
    var_dump($sql->getSqlStringForSqlObject($select));