如果第一行不为空，如何将值插入第二行？ 数据库

Question

I should insert value to parnerCode2 if parnerCodeOwner1 already taken value;

Below code only inserts to parnerCodeOwner1 if new values comes it rewrites first one, It shouldn't rewritten, value should inserted to parnerCode2

<?php
if (isset($_POST['partnerCode'])) {
    // receive all input values from the form
    $partnerCode= mysqli_real_escape_string($db, $_POST['partnerCode']);
    if (empty($partnerCode)) { 
        array_push($errors, "CODE required"); 
    }

    $user_check_query = "SELECT * FROM refer WHERE partnerCode='$partnerCode' LIMIT 1";
    $result = mysqli_query($db, $user_check_query);
    $user = mysqli_fetch_assoc($result);

    if (count($errors) == 0) {
        $query = "update refer set partnerCodeOwner1= '" . $_SESSION['username'] . "'  where randomfield='$partnerCode'  ";
        mysqli_query($db, $query);
    }   
}
?>

ID       randomfield   parnerCode2  parnerCodeOwner1
+-------+-------------+-------------+----------------+
|   1   | uOxerUg4    |             | BuBI9vk        |
+-------+-------------+-------------+----------------+
|   2   | cZzuJlcs    |             | uOxerUg4       |
+-------+-------------+-------------+----------------+
|   3   | BuBI9vke    |             | cZzuJlcs       |
+-------+-------------+-------------+----------------+

Answer 1

You started on the right track with this code:

$user_check_query = "SELECT * FROM refer WHERE partnerCode='$partnerCode' LIMIT 1";
$result = mysqli_query($db, $user_check_query);
$user = mysqli_fetch_assoc($result);

What you actually want is to grab the row that belongs to the user, not the partner. So, your query should be:

$user_check_query = "SELECT partnerCode1 FROM refer WHERE randomField='".$_SESSION['username']."' LIMIT 1";

Once you get the $user row...

if(empty($user['partnerCode1']))

If that is true, insert the partnerCode into partnerCode1. Else, insert it into partnerCode2.

Also, there is no need to fetch the row to check it if there is an error. So, all of that code should come after the if statement that checks for errors.