How do I determine which channel field groups are not being used?

Question

We've created a lot of channels over the years some of which have been pruned back. This potentially leaves their channel field groups as useless clutter.

There doesn't seem to be a view within expression engine that succinctly displays which template groups are used with which channels -- or if any channel field groups are not being used at all.

How do I see which channel field groups are not associated with any channel?

Answer 1

This MySQL query will return a list of all the channel field groups that are not associated with a single channel:

SELECT 
    *
FROM
    exp_field_groups g
WHERE
    NOT EXISTS( SELECT 
            g.group_id
        FROM
            exp_channels c
        WHERE
            g.group_id = c.field_group)