TYPO3: How to display Frontendgroup memberships in backend, felogin Extension - typo3

Question

I have a TYPO3 v10 instance. The felogin Extension is installed to manage 4000 users in 100 usergroups, lots of tiny projects.
Is there a feature, a trick, an extension to answer this question, while working in the backend:
For a given frontenduser-group what are the feusers that belong to that group?
There does not seem to be a way to display this in the backend. At least not in the "List" module, after clicking on any frontendgroup-name, then working in any of the standard tabs "
General / Options / Access / Notes / Extended"
Right now I get along with SQL statements like
SELECT * FROM fe_users WHERE usergroup like '%261%';
but this is very inconvenient.
I have migrated the users and groups from one old TYPO3 instance to a newer one, and now I want to enable editors to cross-check and review group memberships themselves.
The Stackoverflow "Similar questions" text-analysis tool points out that my question is indeed similar to this one: Extbase fe_user findByUsergroup - but that question is 4 Years old, and perhaps there has been some progress?

Answer 1

I know of such "included" feature. The listview offers a "ref" (references) column which shows you all references to this group. this might help a bit. but contains pages, content elements... and user records in a mix.
Another option is the export a CSV of the website users with the "Groups, column enabled. This should give them all the data to review the group memberships.
If that is not enough, I would create an custom module to create such a view.

Answer 2

Meanwhile, as a workaround, I have used a nonstandard-SQL feature, the group_concat() function, to copy all frontendusernames of each group into the (empty) "description" field of the fe_groups table.
There they form a comma-separated list. A screenshot illustrates what my backend panel now looks like. See first line:
This method is only feasible of you are running a one-off migration, or if you can practice on a staging server first. You need to have absolute control over the TYPO3 database, and your bosses and editors shouldn't mind and like the final result. Also it overwrites what is in the description column.
Also, frontendusers who are in two or more groups will NOT get added to the csv-lists! Because their usergroupcolumn has values like 262,398 which cannot be INNER JOINed properly with fe_group.uid.
The key benefit of the group_concat() method is that a single SQL UPDATE statement (almost) solves the problem. No custom PHP programming needed.
/* works on mariadb:10.3 */
UPDATE
fe_groups g,
(
SELECT
usergroup,
GROUP_CONCAT(
u.username
ORDER BY
username SEPARATOR ', '
) AS 'usernames'
from
fe_users u
where
usergroup not like '%,%'
group by
usergroup
) AS user_lookup
SET
g.description = user_lookup.usernames
WHERE
user_lookup.usergroup = g.uid
and user_lookup.usergroup not like '%,%';
The code above does not work on mysql 5.7. There I had to try this instead:
/* works on mysql 5-7 */
SET
session group_concat_max_len = 15000;
create temporary table fe_groups_extrainfo
SELECT
usergroup,
GROUP_CONCAT(
u.username
ORDER BY
username SEPARATOR ', '
) AS 'usernames'
from
fe_users u
where
usergroup not like '%,% and uid > 9'
group by
usergroup
limit
0;
insert into
fe_groups_extrainfo
SELECT
usergroup,
GROUP_CONCAT(
u.username
ORDER BY
username SEPARATOR ', '
) AS 'usernames'
from
fe_users u
where
usergroup not like '%,%'
group by
usergroup;
update
fe_groups g
inner join fe_groups_extrainfo x on g.uid = x.usergroup
set
g.description = x.usernames;
Sorry it is not a single SQL Statement as the mariadb-SQL statement but still simpler as programming a custom TYPO3 extension with a complex backend module.
Update 09/2022:
It is essential to update the TYPO3 Reference Index after using this method (direct db-access with SQL-UPDATE statements).
typo3cms referenceindex:update
Otherwise the "Ref" column in the "List" module view would still show a "-" (meaning 0) users belong in this feuser-group. After updating the refindex the "[Ref]" column will then display the approximate count of feusers.