Creating MySQL query with MyBB to explode a field storing a string

I am currently working with a MyBB set up where I am trying to do an SQL query which can check if a user is part of a certain additional group. However, I am having difficulties.

MyBB stores additional group IDs in one VARCHAR field separated by commas, such as 1,23,27,30,49 etc. I know that in PHP I can explode strings using the comma as a delimiter. I understand that MySQL cannot explode, but I can use substring_index to achieve a similar goal. Point to note each user could have a random list of additional groups, so not all users would be the same.

I am trying this

$stmt = $conn->query('SELECT username, additionalgroups FROM my_users WHERE SUBSTRING_INDEX(30, ',', 1)');
foreach ($stmt as $row)
{
print '<div class="name"><a href="#">' . $row['username'] . '</a></div>';
}


This does not seem to work though. Looking at

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I seem to be following their way of constructing the condition, but I get the following error:

Fatal error: Uncaught PDOException: SQLSTATE[HY000]: General error: mode must be an integer in E:\xampp\htdocs\11thinfantrybrigade.co.uk\orbat.php:180 Stack trace: #0 E:\xampp\htdocs\11thinfantrybrigade.co.uk\orbat.php(180): PDO->query('SELECT username...', ', 1)') #1 {main} thrown in E:\xampp\htdocs\11thinfantrybrigade.co.uk\orbat.php on line 180

Any advice please?

The end goal is to print a list of users that meet that criteria.

Thank you.

$stmt = $conn->query('SELECT username, additionalgroups FROM my_users WHERE SUBSTRING_INDEX(\'30\', \',\', 1)');

Preferably it should be like this as the `,` outside the quotes will cause trouble to PHP.

$query = 'SELECT username FROM my_users WHERE CONCAT(",",additionalgroups,",") LIKE "%,30,%"' ;

$stmt = $conn->query($query);
foreach ($stmt as $row)
{
print '<div class="name"><a href="#">' . $row['username'] . '</a></div>';
}