将符合条件的id查询出来,结果是一个一位数组
$classid = M("product_sort")->where("pid = $pid")->getField("id",true);
ThinkPHP in 查询
//将一维数组转换为字符串,用,号隔开
$classid1 = implode(",",$classid);
//原生的in查询方法
/*$pro = M("product")->query("SELECT * FROM `lc_product` where pid IN(SELECT id FROM `lc_product_sort` WHERE pid = $pid)");*/
$pro = selects("product",array("pid"=>array("in","$classid1")),15,"",15);