sql - Finding missing month from my table -

i have table month column. want find rows have missing month in it.following table:

number month      2016-04-01      2016-06-01      2016-07-01 b      2016-03-01 b      2016-04-01 b      2016-05-01 

from above table want find missing numbers have missing month '2016-05-01' (missing may month)