How to get unique number of employees who make a referral

Summary:

We'd like to know the unique number of employees who have referred at least one candidate and then unique number of candidates that have been referred.

Content (required):

We'd like to know the unique number of employees who have referred at least one candidate and then unique number of candidates that have been referred.

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22B

Code Snippet (add any code snippets that support your topic, if applicable):