Problem with accessing data from database

[witt]

Let's call this page data.php
There's a link to this page that sends it the required variables. Like so:
site.com/data.php?user_id=1&data=hello

[code]
<?php

$user_id = $_GET['user_id'];
$data = $_GET['data'];

require_once ('includes/database_connect.php');

$query = "SELECT data_id FROM database WHERE data=$data AND user_id=$user_id";        
$result = @mysql_query ($query);

if (mysql_num_rows($result) == 1) {
        
        $row = mysql_fetch_array ($result, MYSQL_NUM);
        
                 echo $row[0];
    
    }

?>
[/code]

The expected result would be just the data_id for hello. The error received:

Warning: mysql_num_rows(): supplied argument is not a valid MySQL result resource in /www/data.php on line 11

When the query run is :
[code]
$query = "SELECT data_id FROM database WHERE user_id=$user_id";
[/code]

Everything works fine.

When the query run is :
[code]
$query = "SELECT data_id FROM database WHERE data=$data";
[/code]

The same error is displayed.

This is what the table looks like:

[code]
Table name = database

data_id     user_id       data               data_date
1           1            hello           2006-05-30 18:20:07
[/code]

[hvle]

you need quote around values like this:

$query = "SELECT data_id FROM database WHERE data='$data' AND user_id='$user_id'";

when query is wrong, mysql_query returned a null, and this causing other function to spit out error.

[trq]

You need quotes around your data. Also, dont use the error supressor (@), learn to catch errors yourself.
[code]
<?php

$user_id = $_GET['user_id'];
$data = $_GET['data'];

require_once ('includes/database_connect.php');

$query = "SELECT data_id FROM database WHERE data='$data' AND user_id=$user_id";        
if ($result = mysql_query ($query)) {
  if (mysql_num_rows($result) == 1) {
    $row = mysql_fetch_array ($result, MYSQL_NUM);
    echo $row[0];
  }
} else {
  echo mysql_error();
}
?>
[/code]

[witt]

Ah of course...strings need quotes.