php - 请比较php中的两个变量

Question

我想在mysql表中插入数据，但之前不应该插入..

我尝试比较变量，但它总是失败。

<?PHP
$servername = "localhost";
$username = "root";
$password = "";
$dbname = "sunil_electronics";
$conn = new mysqli($servername, $username, $password, $dbname);
$sql = "SELECT p_id FROM inquirycart WHERE p_id='$pid'";
$result = $conn->query($sql);

// output data of each row
$row = $result->fetch_assoc();
$id = $row['p_id'];

if ($id == $pid) {
    header('Location: ' . $url . '&key1=' . $key . '&info=info');
} else {
    $sql1 = "INSERT INTO inquirycart (p_id,p_name, p_image)
        SELECT p_id, p_name, p_image FROM $key
        WHERE p_id = '$pid'";
    $result1 = $conn->query($sql1);

    header('Location: ' . $url . '&key1=' . $key . '&succ=succ');
}
?>

Answer 1

如果之前未使用过p_id，则查询将不会返回任何行。 $result->fetch_assoc() 将返回 NULL，并且 $row['p_id'] 将失败。

您可以只检查返回的行数。

if ($result->num_rows > 0) {
    header('Location: ' . $url . '&key1=' . $key . '&info=info');
} else {
    ...
}