php怎么调用两张表的数据

				$this->initPackage($arow, false);
				$this->chapters = array();
				$sql = 'SELECT * FROM ' . ddddd_dbprefix('article_a_2'); ddddd_dbprefix('article_a_1') . ' WHERE articleid = ' . intval($this->id) . ' ORDER BY chapterorder ASC';
				$res = $query->execute($sql);

				while ($crow = $query->getRow($res)) {
					$this->chapters[] = $crow;
				}

				$this->createOPF();
			}

php怎么调用两张表的数据？字段都一样，这样写，article_a_2和article_a_1各一篇文章，内容却都一样显示article_a_2的文章内容。怎么解决？？

给表定义一个别名