duplicate entry on database using php

Question

how to check for duplicate entry on a form using php?my front end is c#windows application

I am adding a new user to database using c# and php file.

I have created the following:

my project in c# (form1):

c# coding:

  private void btncreate_Click(object sender, EventArgs e)
  {
 var request = (HttpWebRequest)WebRequest.Create("http://***.**.***.***/response.php");
            request.Method = WebRequestMethods.Http.Post;
            request.ContentType = "application/x-www-form-urlencoded";
            using (var stream = request.GetRequestStream())
            {
                var buffer = Encoding.UTF8.GetBytes("userid= " + txtUserid.Text + " & password=" + txtConformpassword.Text + " & first_name=" + txtFirstname.Text + " & last_name=" + txtLastName.Text + "& role= " + cmbRole.Text + "& active=" + cmbActive.Text + "");
                stream.Write(buffer, 0, buffer.Length);
            }
            var response = (HttpWebResponse)request.GetResponse();
            string result = String.Empty;
            using (var reader = new StreamReader(response.GetResponseStream()))
            {
                result = reader.ReadToEnd();
            }
            txtMessage.Text = result; 
}

my PHP file :response.php

<?php    
$uid = $_POST['userid'];   
$pass = $_POST['password'];   
$fname = $_POST['first_name'];   
$lname = $_POST['last_name'];   
$rol = $_POST['role'];
$act = $_POST['active'];

$conn = new mysqli($servername, $username, $password, $dbname);
if ($conn->connect_error) {
    die("Connection failed: " . $conn->connect_error);
} 

   $sql= "INSERT INTO aster(userid,password,first_name,last_name,role,active)
VALUES('$uid', '$pass', '$fname','$lname','$rol','$act');";

     if ($conn->query($sql)) {
    echo "New record created successfully";
} else {
    echo "Error: " . $sql . "<br>" . $conn->error;
}
$conn->close();
?>

it add data successfully but when i enter the same userid in textbox and click create button i need to get an error message in txtmessage as userid already exists.

i search through googling but i did not got any thing about duplicate entry please refer me some coding

Answer 1

You could extend your response.php to do a select statement before the insert. If you are able to select a record with the given ID, then yield a response (essentially an error code) which your C# application will then interpret and display to the user.

As a side note, since the ID field appears to be numeric, you can simply omit it from your form and let the DB increment it automatically. This would also mean that the user will not have to guess which ID values are available.

Answer 2

you just want that the ID which you have entered should not be inserted at the next time . for that you just need to do one thing. make your id as a primary key in your database table creation , after doing this you will be not able to insert that id again or duplicate entries are not allowed in a primary key.

lemme know if it is useful.

Answer 3

It may not help as much, but I think my explanation will point you to the right direction.

What I would do is:

1. I would use SQL query to check if record exist and if exist then print "Record Exists" Else "Record does not exist". Below the code I post, 'Justin Yen' on PHP posting a quote, make sure you assign that to the field of inputting the username. In your case it's $uid.
2. On PHP, assign the result of sql query to a variable.
3. Create a string variable "Record Exists" and "Record does not exist".
4. compare the string variable you create on step 3 to the result on step 2.

5. I don't know any PHP coding, but you can try to find a way to compare string. But here's an example of checking record exist in SQL:

   Declare @Username varchar(MAX) = 'Justin Yen'
   
   IF EXISTS(select Username from EmployeTable where Username = @Username)
   
   begin print 'Record Exists' end
   
   else
   
   begin print 'Record does not exist' end
   

6. Now all you have to do is if variable match then prompt "Cannot create record because Record created." Else use the add record codes you have in php.

Answer 4

You can simply try to add the contraints(UNIQUE/PRIMARY) to the column 'userid'.

ALTER TABLE aster ADD CONSTRAINT MyUniqueKey UNIQUE KEY(userid)