Why is only one row from this query displayed? - php

Question

I am trying to print the results of this query, but it only prints out the first row. Why is that?
if (isset($_GET['consumiperstanza'])) {
$num_stanza=$_GET['num_stanza'];
$data1=$_GET['data1'];
$data2=$_GET['data2'];
$query="SELECT stanze.num_stanza,consumi.cod_consumo, servizi.nome,
consumi.quantita, servizi.prezzo, consumi.data_c
FROM consumi, servizi, stanze
WHERE stanze.num_stanza=consumi.num_stanza
AND servizi.cod_servizio=consumi.cod_servizio
AND stanze.num_stanza='$num_stanza'
AND consumi.data_c BETWEEN '$data1' AND '$data2'
GROUP BY stanze.num_stanza";
$risultato = $conn->query($query);
if(mysqli_num_rows($risultato) > 0){
echo "<table border=1 bgcolor= 'white' align='center'>";
echo "<tr>";
echo "<th>NUMERO STANZA</th>";
echo "<th>CODICE CONSUMO</th>";
echo "<th>NOME</th>";
echo "<th>QUANTITÀ</th>";
echo "<th>PREZZO</th>";
echo "<th>DATA</th>";
echo "</tr>";
while($riga = mysqli_fetch_array($risultato)){
echo "<tr>";
echo "<td>" . $riga[0] . "</td>";
echo "<td>" . $riga[1] . "</td>";
echo "<td>" . $riga[2] . "</td>";
echo "<td>" . $riga[3] . "</td>";
echo "<td>" . $riga[4] . "</td>";
echo "<td>" . $riga[5] . "</td>";
echo "</tr>";
}
echo "</table><br>";
}
}

Answer 1

This is part of your criteria
AND stanze.num_stanza='$num_stanza'
But you're also doing this.
GROUP BY stanze.num_stanza
So, you'll only get one group.
Additionally, all the other columns in your SELECT are not well-defined since they are not included in the GROUP BY and are not aggregate expressions. Newer versions of MySQL actually will not allow you to do this by default. It is possible in older versions, but may not give you the results you expect.
The MySQL 5.6 manual:
... this is useful primarily when all values in each nonaggregated column not named in the GROUP BY are the same for each group. The server is free to choose any value from each group, so unless they are the same, the values chosen are nondeterministic.