Matching user IDs

I have a particular problem that I haven't been able to find any other posts covering.

I have three datasets with different information. They all have 8 digit user IDs for identification but different columns. There are also a different set of User IDs in each data set but some are found in all 3. These are large datasets with 1000s of User IDs.

I am able to find my User IDs of interest in one dataset, but need data for these User IDs from the other datasets. How can I extract data based on User IDs without searching each one individually? Is there a way to match them?

Thank you