why code users_online is auto increment when refresh

[FaN_Vw]

when i refresh this page users is auto increment\[code\]<? $session= session_id(); $time=time(); $time_check=$time-600; //SET TIME 10 Minute include "conf.php" ; $tbl_name="user_online"; /// Table name //search for session id in database $result=mysql_query("SELECT * FROM $tbl_name WHERE session='$session'" ); $count=mysql_num_rows($result); if($count=="0"){ // if not found insert $result1=mysql_query("INSERT INTO $tbl_name(session, time)VALUES('$session', '$time')"); } else { // if found update data $result2=mysql_query("UPDATE $tbl_name SET time='$time' WHERE session = '$session'"); } $result3=mysql_query("SELECT * FROM $tbl_name"); $count_user_online=mysql_num_rows($result3); echo "User online : $count_user_online "; // if over 10 minute, delete session $result4=mysql_query("DELETE FROM $tbl_name WHERE time<$time_check"); mysql_close(); // Open multiple browser page for result ?>\[/code\]