Show all church names except or those that had a wedding in year 2015.
SELECT name FROM church EXCEPT SELECT T1.name FROM church AS T1 JOIN wedding AS T2 ON T1.church_id   =   T2.church_id WHERE T2.year   =   2015
church names = SELECT name FROM church; excluding those with a wedding in 2015 = EXCEPT SELECT ... WHERE T2.year = 2015;