Here's some sample data (which you should have posted) and a shorter version of your query.

What should the results look like for this data?

CREATE TABLE POSTING(

POSTING_ID INT IDENTITY(1,1),

CREATE_DATE DATETIME

);

INSERT INTO POSTING

VALUES

('20140101'),

('20140201'),

('20140301'),

('20140401'),

('20140501'),

('20140101'),

('20150201'),

('20150211'),

('20150301'),

('20150311'),

('20150401'),

('20150411'),

('20150501'),

('20150511'),

('20150601'),

('20150711'),

('20160101'),

('20160111'),

('20160201'),

('20160211');

SELECT *

FROM POSTING;

SELECT DATEADD(mm, DATEDIFF(mm, 0, CREATE_DATE), 0) AS THEDATE

, YEAR(post.CREATE_DATE) AS THEYEAR

, MONTH(post.CREATE_DATE) AS THEMONTH

, STUFF(CONVERT( VARCHAR(11), post.create_date), 4, 4, '-') AS [Month-Year]

, COUNT(DISTINCT post.POSTING_ID) AS POST_PERF

FROM POSTING AS post

WHERE post.CREATE_DATE >= '20150101'

AND post.CREATE_DATE < '20160201'

GROUP BY DATEADD(mm, DATEDIFF(mm, 0, CREATE_DATE), 0)

, YEAR(post.CREATE_DATE)

, MONTH(post.CREATE_DATE)

, STUFF(CONVERT( VARCHAR(11), post.create_date), 4, 4, '-');

GO

DROP TABLE POSTING;

Why are you using NOLOCK hints? Are you aware of the risks of bringing incorrect data?