Help: Unable to get a student written to database more than once

[belbin09]

Hi, I am almost done my assignment however I am having an issue. I am trying to read enrolment and if the student is already registered for the course then print an error. However I am only able to register one student in one course each before getting the error message, which leads me to believe that it isn't reading the enrolment file properly. I seam to have an issue with this. Any help would be grateful. Thank you

 

// if the course is found and the student is found then check if they have registered
if ($found==3) {


  $equery= "SELECT * FROM enrolment WHERE uid ='$number' AND code = '$course'";
  $eresult= mysqli_query($link, $equery);


  while ($erow = mysqli_fetch_array($eresult)) {
  if ($erow['code'] == $course && $number == ($erow['uid'])) {


  
    } // if ($erow['code'] == $course && $number == ($erow['uid']))
  } // while ($erow = mysqli_fetch_array($eresult))
} // if ($found==3)


//if the student isn't registered in the course


$equery = "INSERT INTO enrolment(uid,code) VALUES ('$number','$course')";


if (mysqli_query($link, $equery)) {
  echo "New record created successfully";
}// if (mysqli_query($link, $equery))
else {
  echo "Error: You have already registered for the course";
} // else echo "Error: " .$link->error;


mysqli_close ($link);

 

[phpmillion]

The logic of your script is wrong. Here's how the proper logic should look like:

 

<?php


// if the course is found and the student is found then check if they have registered
if ($found==3)
    {
    $equery= "SELECT * FROM enrolment WHERE uid ='$number' AND code = '$course'";
    //NOW YOU NEED TO COUNT THE NUMBER OF RETURNED RESULTS
  
    if ($NUMBER_OF_RETURNED_RESULTS>0)
        {
        echo "Error: You have already registered for the course";
        }
    else
        {
        //RUN QUERY TO INSERT DATA
        //IF QUERY SUCCEDED, DISPLAY SUCCESS MESSAGE 'New record created successfully'
        }
    }

 

As you see, I didn't post the whole code, but you get the idea. Also, be aware that the way you use MySQL queries now is very risky, since anyone could hack your database.

[requinix]

Put the error message output back in for a minute.

else {
  // echo "Error: You have already registered for the course";
  echo "Error: " .$link->error;
}

What does it say?

[belbin09]

Put the error message output back in for a minute.

else {
  // echo "Error: You have already registered for the course";
  echo "Error: " .$link->error;
}

What does it say?

 

 

Error: Duplicate entry '123456789' for key 'PRIMARY'

[belbin09]

Removed the PRIMARY KEY from uid now it is registering the student for the same course

[Barand]

Make the primary key on both columns

PRIMARY KEY (uid, code)

Now you can have as many records for a student as you want but you won't be allowed to add a course twice for the same student.

 

This also saves you having to do the select query first. Just insert the student/code combination. If you get a "duplicate key" error you can warn them they are already enrolled.