I have two datasets and I want to make sure that the same IDnumber has not been recorded twice in the two different data sets (They are two different stata files). See example below. Variable name is IDnumber. How can I ask stata to highlight where the same IDnumber has been recorded twice. for example in this data set, IDnumber 1 and 3 have been recorded twice and I would like stata to list these for me.
Eg.
Dataset1
IDnumber
1
2
3
4
5

Dataset2
IDnumber
1
3
6
7
8

Thanks very much