--Get list of URLs in table 1 not present in table 2
select * from table_1 where URL not in (select URL from table_2)

--Get list of URLs in both tables
select T1.URL
from table_1 T1
join table_2 T2 on T1.URL = T2.URL

--Same, but where "description" doesn't match
select T1.URL
from table_1 T1
join table_2 T2 on T1.URL = T2.URL
where T1.Description != T2.Description