php获得sybase数据库内容的有关问题

php获得sybase数据库内容的问题
数据库连接已经测试过了没问题，sql语句也没问题。现在问题是获取不到数据库里的数据，代码如下：

public static function Connect()

 {

 $obj =new DB();

 $conn=$obj->Connection=sybase_connect(SERVER_NAME, USER, PASSWORD) ; // 连接数据库

 if(!$conn){

 echo '数据库连接错误...';

 exit(0);

 }

 sybase_select_db(DATABASE_NAME);

     return $obj;  

 }

 //初始化页面时查询最近一个月的销售记录

 public function QueryLastMonth(){

 $start_date=str_replace('-','',date('Y-m-d',strtotime('-1 month')));

 $end_date=str_replace('-','',date('Y-m-d',time()));

 $sql_str="select cusno as shopcode,u2.nos as salesid,u2.colthno as goodsid,u2.endprice as price,u2.nb as goodscount from u2sale u1,u2saleb u2 where u1.outdate>=";

$sql=$sql_str ."'".$start_date."' and u1.outdate<='".$end_date."' and u1.nos=u2.nos and u1.nb>0 and u2.endprice>0;";



  //echo $sql;

 // sybase_query("set rowcount " . 20) ; // 执行SQL命令，设置返回记录行数

   $result = sybase_query($sql) ; // 执行SQL命令，检索数据库

   echo "---".$result;

   while($row = sybase_fetch_assoc($result)) 

   { 

  // echo 'xxx';

   echo $row["shopcode"] . "---" . $row["salesid"] . "---" . $row["goodscount"] . "\n" ;

    }

	

	sybase_close($conn);

 }