Selecting rows within N days of range of certain records

Question

I need to get the records which are in a range of 20 days following a certain process.

There is a table medical that contains data as shown below:

Here is the SQLFIDDLE:

Rule is : If Group is A3, then all operations within 20 days (to the same patient in the same hospital) are free of charge.

So, here all the operations until 09.02.2013 should be free of charge. (20.01.2013 + 20 days)

Question: How can I retrieve all the records within 20 days following the day an A3 group process is applied?

Answer 1

I took the liberty of changing the datatype of dat and changed the name of group to groupe.

WITH modified_medical
     AS (SELECT hospital, pid, dat
           FROM medical
          WHERE groupe = 'A3')
  SELECT *
    FROM medical a, modified_medical b
   WHERE     b.hospital = a.hospital
         AND b.pid = a.pid
         AND a.dat BETWEEN b.dat AND b.dat + 20
ORDER BY a.hospital, a.pid, a.dat;

Sample fiddle here.