mysqli_query（）至少需要2个参数和mysqli_query（）：空查询错误消息

代替

$query = mysqli_query("SELECt * FROM subscriptions WHERe email='$email'");

采用

$query = $con->query("SELECt * FROM subscriptions WHERe email='$email'");

要么

$query = mysqli_query($con, "SELECt * FROM subscriptions WHERe email='$email'");

也代替

$insert_email = mysqli_query("INSERT INTO subscriptions (email) VALUES ('$email')");

采用

$insert_email = $con->query("INSERT INTO subscriptions (email) VALUES ('$email')");

这些是我可以看到的仅有的两个错误。