如何检查用户是否已经在我的网络应用程序中使用 Google+API 登录过？

Yes,Add authprovider field in your table.
When any user login with google at first time then store google in your database.
After than when user Login again then use query like this:

$query = "SELECT authprovider,email FROM tbl_users WHERE authprovider='$authprovider' AND email='$email'";
$exe = mysqli_query($conn,$query);
$check = mysqli_num_rows($exe);
if($check == 1){
  //already registered
}
else{
 //new register
}