How can I alert a user that an entry has already been input into the database?

Question

I'm currently trying to ensure no duplicate emails are allowed to be entered within my mySQL database, I've marked stud_email as unique within the database I'm just struggling to alert the message. This is what I've got so far, am I on the correct path?

if (isset($_POST['submit'])) {
    $email = $_POST['email'];

    $check = mysqli_query($conn, "SELECT * FROM students WHERE stud_email = '$email'");
    $checkrows = mysqli_num_rows($check);

    if ($checkrows > 0) {
        echo '<script>alert("Student email already exists")</script>';
    } else {

Possible duplicate of [Prevent duplicate data being entered into mysql database](https://stackoverflow.com/questions/20081424/prevent-duplicate-data-being-entered-into-mysql-database) — Masivuye Cokile, Mar 08 '18 at 12:03
call that email specifically , using : select email from students where email = check email and then continue. — , Mar 08 '18 at 12:24
I believe OP is asking how to (accurately) detect a DUPLICATE KEY error from the database. This is not a duplicate of "Prevent duplicate data being entered into mysql database" — RandomSeed, Mar 08 '18 at 13:26
Does this answer your question? [How to check if a row exists in MySQL? (i.e. check if an email exists in MySQL)](https://stackoverflow.com/questions/22252904/how-to-check-if-a-row-exists-in-mysql-i-e-check-if-an-email-exists-in-mysql) — Dharman, Feb 26 '20 at 20:19

vinieth · Answer 1 · 2018-03-08T12:12:03.387

-2

$check = mysqli_query (SELECT count(*) FROM students WHERE stud_email = '$email');

Use Count to check whether the email is already in your database. If the count is greater than 1 then check it using IF condition in your JSP

if($check>0) {
     echo '<script>alert("Student email already exists")</script>';
}

edited Mar 08 '18 at 12:12

answered Mar 08 '18 at 12:03

vinieth

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I'm now getting this error 'mysqli_num_rows() expects parameter 1 to be mysqli_result' on the $checkrows=mysqli_num_rows($check); line? do you know why this would be – thomas walker Mar 08 '18 at 12:09
you need not need this line `$checkrows=mysqli_num_rows($check);` – vinieth Mar 08 '18 at 12:12
I'm not getting any errors now but I don't get any alert messages @vinieth – thomas walker Mar 08 '18 at 12:18
@thomaswalker Did you check that `$check` returning value > 0. Check that by printing it – vinieth Mar 08 '18 at 12:37

How can I alert a user that an entry has already been input into the database?

1 Answers1