Question

I would like to get the number of rows that satisfies the condition.

mysql_query("SELECT COUNT(*) FROM sid WHERE sid='".session_id()."'");

this one ignores the condition.

update:

$session = session_id();
$sql = "SELECT COUNT(*) as row_count FROM sid WHERE sid = '$session' ";
var_dump($r = mysql_query($sql));//resource(4) of type (mysql result) (1)
var_dump(mysql_fetch_assoc($r));
//array(1) { ["row_count"]=> string(1) "1" }  - this result is OK(2)

(1) resource(4) – I thought that 4 was the count

(2) mysql_real_escape_string($_SESSION['id']); gives 0

note:

I have changed from mysql_num_rows to this type of getting count because I thought it will return immediately the count and I dont have to write more lines to get this basic data.

Answer 1

The correct way of doing this is:

$session = mysql_real_escape_string($_SESSION['id']);  <<-- Get the session id
echo "debug: session_id = ".htmlentities($session);
$sql = "SELECT count(*) as row_count FROM tablename WHERE sid = '$session' ";
$result = mysql_query($sql);
if (!$result) {
  die('error in query '.$sql.' error is: '.mysql_error());
}
//we only have 1 result
$row = mysql_fetch_array($result);
//always sanitize so you don't suffer XSS attacks when the query changes   
//and the $row['x'] changes from an integer to a user-supplied string.
$count = intval($row['row_count']);  
echo "count is: ".$count;

The table name and the column name can be the same, but in your case they probably are not.
sid obviously stands for the field “session_id”, so you need to replace the first sid after FROM with your tablename.