Hello, I am relative to Stata and I just cannot figure out how to solve the following problem.

My master data set contains household information and my using data contains numbers of events per province per year

(Master data)
year hhid province
2008 1097 province A
2008 2097 province A
2008 3524 province A
2008 2015 province B
2009 7020 province B
2009 7020 province B
2008 5214 province C

(Using dataset)
year province #events
2008 province A 245
2008 province B 458
2008 province C 344
2009 province A 312
2009 province B 765

I want to add the using dataset into the master data so that for every year province the number of events is added to those observations. My attempts with merge and joinby have so far not been successful, because it requires uniquely identified observations. How can I merge the using data into the masterdata and add the number of events to every matching year province observation? I am certain there is an easy solution to it, but I have not found it yet.

Thanks