通过PHP从MySQL数据库中检索行

Please bear with me, I'm new here - and I'm just starting out with PHP. To be honest, this is my first project, so please be merciful. :)

    $row = mysql_fetch_array(mysql_query("SELECT message FROM data WHERE code = '". (int) $code ."'         LIMIT 1"));
    echo $row['message'];

Would this be enough to fetch the message from the database based upon a pre-defined '$code' variable? I have already successfully connected to the database.

This block of code seems to return nothing - just a blank space. :(

I would be grateful of any suggestions and help. :)

UPDATE:

Code now reads:

    <?php
    error_reporting(E_ALL);
   // Start MySQL Connection
    REMOVED FOR SECURITY
    // Check if code exists
    if(mysql_num_rows(mysql_query("SELECT code FROM data WHERE code = '$code'"))){
    echo 'Hooray, that works!';
    $row = mysql_fetch_array(mysql_query("SELECT message FROM data WHERE code = '". (int) $code     ."' LIMIT 1")) or die(mysql_error());
    echo $row['message'];
    }
    else {
    echo 'That code could not be found. Please try again!';
    }
    mysql_close();
    ?>

It's best not to chain functions together like this since if the query fails the fetch will also appear to fail and cause an error message that may not actually indicate what the real problem was.

Also, don't wrap quotes around integer values in your SQL queries.

if(! $rs = mysql_query("SELECT message FROM data WHERE code = ". (int) $code ." LIMIT 1") ) {
    die('query failed! ' . mysql_error());
}
$row = mysql_fetch_array($rs);
echo $row['message'];

And the standard "don't use mysql_* functions because deprecated blah blah blah"...

If you're still getting a blank response you might want to check that you're not getting 0 rows returned. Further testing would also include echoing out the query to see if it's formed properly, and running it yourself to see if it's returning the correct data.

Some comments:

1. Don't use mysql_*. It's deprecated. use either mysqli_* functions or the PDO Library
2. Whenever you enter a value into a query (here, $code), use either mysqli_real_escape_string or PDO's quote function to prevent SQL injection
3. Always check for errors.

Example using PDO:

//connect to database
$user = 'dbuser';  //mysql user name
$pass = 'dbpass';  //mysql password
$db   = 'dbname';  //name of mysql database
$dsn = 'mysql:host=localhost;dbname='.$db;
try {
    $con = new PDO($dsn, $user, $pass);
} catch (PDOException $e) {
    echo 'Could not connect to database: ' . $e->getMessage();
    die();
}

//escape code to prevent SQL injection
$code = $con->quote($code);
//prepare the SQL string
$sql = 'SELECT message FROM data WHERE code='.$code.' LIMIT 1';
//do the sql query
$res = $con->query($sql);
if(!$res) {
    echo "something wrong with the query!";
    echo $sql; //for development only; don't output SQL in live server!
    die();
}
//get result
$row = $res->fetch(PDO::FETCH_ASSOC);
//output result
print_r($row);