Creating a date table using only months and years

How to create a date table using only month and years? I can't filter my current date by days table because it was created using a formula.

Example:

ID         Year  Month  MonthNumber

201501 2015 January   01

201502 2015 February 02

201503 2015 March     03

etc.

Reason being, to retrieve google analytics data over a long period of time by days (ga:date) it doesn't return more than a couple of months. Though if retrieved by month it appears to retrieve data that goes further back. Though I still need to create relations to a date table, which I cannot do to the regular date table with days since it needs unique values.

Any help much appreciated.