Il vous suffit de préciser sur quelles tables appliquer le DELETE .
Supprimer uniquement le deadline lignes :
DELETE `deadline` FROM `deadline` LEFT JOIN `job` ....
Supprimer le deadline et job lignes :
DELETE `deadline`, `job` FROM `deadline` LEFT JOIN `job` ....
Supprimer uniquement le job lignes :
DELETE `job` FROM `deadline` LEFT JOIN `job` ....