Is this what you mean?
SELECT
dcea4_eb_events.event_date,
dcea4_eb_events.title,
dcea4_eb_registrants.id,
dcea4_eb_registrants.first_name,
dcea4_eb_registrants.last_name,
dcea4_eb_registrants.email,
dcea4_eb_registrants.register_date,
dcea4_eb_registrants.amount,
dcea4_eb_registrants.comment,
Group_Concat( concat("id=",field_id," value=,field_value") ) as "IDs/VALUES"
FROM dcea4_eb_events
JOIN dcea4_eb_registrants ON dcea4_eb_registrants.event_id = dcea4_eb_events.id
JOIN dcea4_eb_field_values ON dcea4_eb_field_values.registrant_id = dcea4_eb_registrants.id
WHERE 1=1
AND dcea4_eb_field_values.field_id IN(14,26,27,15)
AND dcea4_eb_registrants.published <> 2
AND dcea4_eb_registrants.published IS NOT NULL
AND (dcea4_eb_registrants.published = 1 OR dcea4_eb_registrants.payment_method = "os_offline")
[ AND (dcea4_eb_registrants.register_date {RegistrationDate} ) ]
[ AND REPLACE(dcea4_eb_events.title,'\'','') in ({Club}) ]
GROUP BY dcea4_eb_events.event_date,dcea4_eb_events.title,dcea4_eb_registrants.id,
dcea4_eb_registrants.first_name,dcea4_eb_registrants.last_name,
dcea4_eb_registrants.email,dcea4_eb_registrants.register_date,
dcea4_eb_registrants.amount,dcea4_eb_registrants.comment
ORDER BY dcea4_eb_registrants.register_date,dcea4_eb_events.title;
If not, please post Show Create Table results for the tables and enough sample Inserts to generate a result.