Someone

REPLACE INTO itm_event_artist 
SELECT ies.ID AS itm_event_id, ia.id AS itm_artist_id FROM itm_events ies INNER JOIN itm_artist ia ON replace(substring(substring_index(ies.djs, ',', 1),
                         length(substring_index(ies.djs, 
                                                ',', 
                                                1 - 1)) + 1),
               ',', '') = ia.name

REPLACE INTO itm_event_artist 
SELECT ies.ID AS itm_event_id, ia.id AS itm_artist_id FROM itm_events ies INNER JOIN itm_artist ia ON replace(substring(substring_index(ies.djs, ',', 2),
                         length(substring_index(ies.djs, 
                                                ',', 
                                                2 - 1)) + 1),
               ',', '') = ia.name

REPLACE INTO itm_event_artist 
SELECT ies.ID AS itm_event_id, ia.id AS itm_artist_id FROM itm_events ies INNER JOIN itm_artist ia ON replace(substring(substring_index(ies.djs, ',', 3),
                         length(substring_index(ies.djs, 
                                                ',', 
                                                3 - 1)) + 1),
               ',', '') = ia.name

REPLACE INTO itm_event_artist 
SELECT ies.ID AS itm_event_id, ia.id AS itm_artist_id FROM itm_events ies INNER JOIN itm_artist ia ON replace(substring(substring_index(ies.djs, ',', 4),
                         length(substring_index(ies.djs, 
                                                ',', 
                                                4 - 1)) + 1),
               ',', '') = ia.name

REPLACE INTO itm_event_artist 
SELECT ies.ID AS itm_event_id, ia.id AS itm_artist_id FROM itm_events ies INNER JOIN itm_artist ia ON replace(substring(substring_index(ies.djs, ',', 5),
                         length(substring_index(ies.djs, 
                                                ',', 
                                                5 - 1)) + 1),
               ',', '') = ia.name