"Undefined variable" error

Question

I’m trying to run this code but it’s not working.

$sql    = "SELECT * FROM cliente WHERE id = $id ";
$limite = mysql_query("$sql");

while ($sql = mysql_fetch_array($limite)){

    $nome       = $sql["nome"];
    $telefone   = $sql["telefone"];

    $id         = $_GET['id'];

    echo "<div class='clientecelula'>" ;
    echo "$nome"; 
    echo "<span class='telcelula'> $telefone </span>";
    echo "<span class='semcelula'>  </span>";
    echo "</div>" ; 

}

I’m getting the bug:

Notice: Undefined variable: id in /Applications/XAMPP/xamppfiles/htdocs/Ross/semana.php on line 7

Warning: mysql_fetch_array() expects Parameter 1 to be Resource, Boolean Given in /Applications/XAMPP/xamppfiles/htdocs/Ross/semana.php on line 12

What’s the problem here?

Answer 1

Your problem is in the variable $id that is assigned after it is already being used in SQL.

If you change places, you’ll figure it out that problem:

$id     = $_GET['id'];
$sql    = "SELECT * FROM cliente WHERE id = $id ";
$limite = mysql_query($sql);

while ($sql = mysql_fetch_array($limite))
{
    $nome       = $sql["nome"];
    $telefone   = $sql["telefone"];

    echo "<div class='clientecelula'>" ;
    echo "$nome"; 
    echo "<span class='telcelula'> $telefone </span>";
    echo "<span class='semcelula'>  </span>";
    echo "</div>" ; 

}

IMPORTANT: I advise the use of functions of type mysqli_ because the functions of the type mysql_ will be discontinued as you can see in this question.

Answer 2

Notice: Undefined variable

says the variable does not exist and in the code displayed in the question $id is defined after the query has been executed and you need it before that, as it will be used as an argument in SQL be sure to check if its value is valid, force a cast for whole.

Prefer mysql_query($sql) or die(mysqsl_error()) in place of mysql_query($sql); the first way will display the database error message if the query fails that can be from a syntax error to some other more serious problem.

>>#a última linha do while deveria estar aqui<<

$sql    = "SELECT * FROM cliente WHERE id = $id ";
$limite = mysql_query("$sql");

while ($sql = mysql_fetch_array($limite)){
    $nome       = $sql["nome"];
    $telefone   = $sql["telefone"];
    $id         = $_GET['id'];    <----- essa linha deveria estar antes da atribuição de $sql
}

The corrected code looks like this:

$id = (isset($_GET['id'])) ? $_GET['id'] : 0;

$sql    = "SELECT * FROM cliente WHERE id = $id ";
$limite = mysql_query($sql) or die(mysql_error());

while ($sql = mysql_fetch_array($limite)){
    $nome       = $sql["nome"];
    $telefone   = $sql["telefone"];
    $id         = $sql['id'];
}

If the code is from a new project it is highly recommended to use mysqli or PDO. Recommended reading:

Why should we not use mysql type functions_*?

Mysqli vs PDO - which is the most recommended to use?