BEGIN
DROP TABLE IF EXISTS attendeesWithCustomFields;
SET @SQL = NULL;
SELECT GROUP_CONCAT( DISTINCT
        CONCAT(
            'MIN(CASE WHEN cf.field_name = ''',
            field_name,
            ''' THEN cf.field_value END) AS ',
            field_name
        )
    ) INTO @SQL
FROM custom_fields;
SET @SQL = CONCAT(  'CREATE TABLE attendeesWithCustomFields
                    SELECT a.* , ', @SQL , '
                   FROM attendees a
                   LEFT JOIN custom_fields AS cf
                    ON cf.event_id = a.event_id AND cf.investor_id = a.investor_id
                    GROUP BY a.event_id, a.investor_id ' );
PREPARE stmt FROM @SQL;
EXECUTE stmt;
DEALLOCATE PREPARE stmt;
END