How to convert two dates into month format

Hi,
Lets say we have two dates 2012-10-10 and 2012-12-31. I want to make a data entry into a table like this
Start Date                 End Date
2012-10-10               2012-10-31
2012-11-01               2012-11-30
2012-12-01               2012-12-31
Any code or algorithm will be appricated.
Thanks
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