Checking for valid email and if it exists

Question

I have successfully been able to allow users to invite a friend by sending them an email with a unique invite code,

• however I am trying to add to ability to c

Answer 1

I think your main question is how to check if an email exists in another table. If that's wrong, let me know and I can update my answer :P Here's a rough draft of a function you should be able to use.

I'm assuming you have these two tables:

Table 1: users

||id||email||name||

Table 2: invites

||id||email||inviter_user_id||

You can use this function to check if the email exists in either table

<?php
    /**
     * Check if the given email already exists in the DB
     *
     * @param $email string the email to check
     */
    function email_exists($email)
    {
        if (!empty($email)) {
            $ret_val = false;

            $query = sprintf(
                "SELECT id FROM users WHERE email = '%s'",
                mysqli_real_escape_string($email)
            );

            $result = mysqli_query($query);
            $num_rows = mysqli_num_rows($result);
            if ($num_rows > 0) {
                //email exists
                $ret_val = true;
            } else {
                $query = sprintf(
                    "SELECT id FROM invites WHERE email = '%s'",
                    mysqli_real_escape_string($email)
                );

                $result = mysqli_query($query);
                $num_rows = mysqli_num_rows($result);
                if ($num_rows > 0) {
                    //email exists
                    $ret_val = true;
                }
            }
            return $ret_val;
        }
    }
?>