mysql_query()
does not support multiple statements like 1) SET @rownr=0;
2) your query for this you can rewrite your query as below
SELECT
TVGD.video_id,
TVM.Video_Title,
@rownr := @rownr + 1 AS `Order`,
'0' AS Min_Pass_Mark
FROM
tbl_video_group_details TVGD,
tbl_Video_Master TVM ,
(SELECT @rownr := 0) t
WHERE TVGD.video_id = TVM.id
AND TVGD.group_id = '23'
or you can use mysqli::multi_query which does support multiple statements