Php 从oracle的oci_num_行返回的结果为零

当我执行这个查询时，oci_num_行的结果总是为零，有人能帮忙吗

  $sql="SELECT * FROM apps.xx_fa_by_loc_mob where site_name ='$location' AND  tag_number='$data1'";

$res= oci_parse($link, $sql);
oci_execute($res);

$var=oci_num_rows($res);
echo $var;

任何帮助都会很好

这可能是：

Note:

This function does not return number of rows selected! For SELECT statements this function will return the number of rows, that were fetched to the buffer with oci_fetch*() functions.