//用法1,用join:根据表the2的id和表the2_pic的parentid相等,并且the2_pic的iscover是1,取表2的src
$sql = "select the2.*,the2_pic.src from the2 LEFT JOIN the2_pic ON the2.id=the2_pic.parentid and the2_pic.iscover=1 order by the2.time";
//用法2,用where:
$sql = "select the2.*,the2_pic.src from where the2.id=the2_pic.parentid order by the2.time";