Change input radio value in multiple row update form

Question

I can't changed the value in a row inside of my DB, when I select another radio different of the checked in the update form... always returns the previous state... How can I make it works?

Here are the captures:

1. How the radio is checked

2. The success message

But when I refresh the window, the checked input is always the previous one.

Here is the code:

//form:

.....
    <td>
        <input type="text" value="<?php echo $venta; ?>" name="venta[]" id="venta_<?php echo $i; ?>" class="form-control" autocomplete="off" placeholder="Precio de venta" required="required"/>
    </td>
    <td>
        <input type="radio" name="principal[]" id="principal_<?php echo $i; ?>" <?php if($principal == 1){ echo 'value="0" checked="checked"';} else { echo 'value="1"';}; ?>>
    </td>
.....
</tr>

//the insert/update code:

$sql = "INSERT INTO MEDIDAS (idMed, principal, cod, presentacion, cantidad, compra, venta, id_user)
 VALUES ";
$insertQuery = array();
$insertData = array();
foreach ($_POST['venta'] as $i => $venta) {
    $insertQuery[] = '(?, ?, ?, ?, ?, ?, ?, ?)';
    $insertData[] = $_POST['idMed'][$i] == '' ? null : $_POST['idMed'][$i];
    $insertData[] = $_POST['principal'][$i] == '' ? 0 : $_POST['principal'][$i]; //this is the row with the input radio
    $insertData[] = $code;
    $insertData[] = $_POST['presentacion'][$i];
    $insertData[] = $_POST['existencia1'][$i];
    $insertData[] = $_POST['compra'][$i];
    $insertData[] = $_POST['venta'][$i];
    $insertData[] = $id_user;
}
if (!empty($insertQuery)) {
    $sql .= implode(', ', $insertQuery);
    $sql .= " ON DUPLICATE KEY UPDATE
    principal = VALUES (principal), cod = VALUES (cod), presentacion = VALUES (presentacion), cantidad = VALUES (cantidad),
    compra = VALUES (compra), venta = VALUES (venta), id_user = VALUES (id_user)
    ";
    $stmt = $conn->prepare($sql);
    $stmt->execute($insertData);
}

Answer 1

Only the checked radio button is sent to the server. So you don't get a parameter for each row, there's just one value for the entire form. So it shouldn't use a [] name.

Instead, give each button a value with the row index.

    <td>
        <input type="radio" name="principal" id="principal_<?php echo $i; ?>" value="<?php echo $i; ?>" <?php if($principal == 1){ echo 'checked="checked"';} ?>>
    </td>

Then in your loop when processing the form you can check whether the value of the radio button matches the index of the loop.

foreach ($_POST['venta'] as $i => $venta) {
    $insertQuery[] = '(?, ?, ?, ?, ?, ?, ?, ?)';
    $insertData[] = $_POST['idMed'][$i] == '' ? null : $_POST['idMed'][$i];
    $insertData[] = $_POST['principal'] == $i ? 1 : 0;
    $insertData[] = $code;
    $insertData[] = $_POST['presentacion'][$i];
    $insertData[] = $_POST['existencia1'][$i];
    $insertData[] = $_POST['compra'][$i];
    $insertData[] = $_POST['venta'][$i];
    $insertData[] = $id_user;
}