Get last 12 months data from Db with year in Postgres

I believe you wanted this:

SELECT to_char(revision_timestamp, 'YYYY-MM'),       count(b.id)FROM package aJOIN package_revision b ON a.revision_id = b.revision_idWHERE revision_timestamp >      date_trunc('month', CURRENT_DATE) - INTERVAL '1 year'GROUP BY 1

select    count(B.id),    date_part('year', revision_timestamp) as year,    date_part('month',revision_timestamp) as monthfrom package as A    inner join package_revision as B on A.revision_id=B.revision_id where    revision_timestamp > (current_date - INTERVAL '12 months') group by    date_part('year', revision_timestamp)    date_part('month', revision_timestamp)

or

select    count(B.id),    to_char(revision_timestamp, 'YYYY-MM') as monthfrom package as A    inner join package_revision as B on A.revision_id=B.revision_id where    revision_timestamp > (current_date - INTERVAL '12 months') group by    to_char(revision_timestamp, 'YYYY-MM')

Keep in mind that, if you filter by revision_timestamp > (current_date - INTERVAL '12 months'), you'll get range from current date in last year (so if today is '2013-09-04' you'll get range from '2012-09-04')