SELECT A.column2
, B.column2
, C.column2
FROM
(
(SELECT month, column2 FROM table1) A
FULL OUTER JOIN
(SELECT month, column2 FROM table2) B on A.month= B.month
FULL OUTER JOIN
(SELECT month, column2 FROM table3) C on ISNULL(A.month, B.month) = C.month
)