Stačí:

SELECT entry_state, address_book_id AS address_book_id, entry_company AS entry_company, p.id_adresy, p.id_skupiny checkbox_checked, 'address_book'
FROM address_book 
LEFT JOIN skupina_obsah p ON p.id_adresy = address_book.address_book_id
AND id_skupiny = 14
WHERE entry_state NOT LIKE ' ' Group by entry_state
UNION Select email , '', '','','', 'bulletin_registr' from bulletin_registr where email NOT LIKE ' ' Group by email