support_calls(call_id, user_id, issue_type, called_at)

For each issue type in September 2026, return what percentage of the users who contacted support about it did so at least twice.

Return issue_type and repeat_user_pct rounded to two decimals, ordered by issue_type.

The denominator is distinct users for that issue, not calls, so a single user calling five times is one user, not five.

Tables

support_calls

call_id  user_id  issue_type  called_at
-------  -------  ----------  -------------------
1        10       billing     2026-09-01 10:00:00
2        10       billing     2026-09-02 10:00:00
3        11       billing     2026-09-03 10:00:00
4        12       login       2026-09-01 10:00:00
5        12       login       2026-09-02 10:00:00
6        12       login       2026-09-03 10:00:00
7        12       login       2026-09-04 10:00:00
8        12       login       2026-09-05 10:00:00
... 2 more row(s)

Expected result

issue_type  repeat_user_pct
----------  ---------------
billing     50.00
login       100.00
shipping    0.00