how to count using proc sql certain conditions

Question

I have a dataset (patients) as such:

Pat_ID     Hos     Date

A              11        1/1/2012

B              12         2/3/2012

B              13         2/3/2012

C              11         4/1/2012

C               11         4/5/2012

How do I count using proc sql such that the outcome looks something like this:

Pat_ID      Visits

A                 1

B                 1

C                 2

Since B has two visits on the same date, they are considered as only 1 visit, whereas C has 2 visits because they are on different dates.

Answer 1

select Pat_ID, count(distinct VisitDate) as Visits
from patient
group by Pat_ID
order by Pat_ID asc