Dear statalisters,

I am trying to merge two datasets and I have some problems. I started yesterday merging using
Code:
joinby firm
and everything was ok. Today I am trying to use
Code:
joinby country year
but I have a problem, I think I créate duplicate data. My master data has 1 million observation and a size about 1,3 GB and the second database is about 170,000 observation and a size of 10MB. The final database is about 20 GB and 20 millón observations.

Do you know why is that change in size and observations? I think there are some duplicates, how can I see if there are duplicates and what can I do if there are?

Thank you very much for your help.

Alejandro