Question

I want to select patient_id and date difference from below table:

p_id    TreatmentDate
15      2008-05-01
15      2008-05-03
15      2008-05-05
15      2008-05-07
16      2008-05-01
16      2008-05-03
16      2008-05-05
16      2008-05-09
16      2008-05-11
17      2008-05-03
17      2008-05-05
17      2008-05-07

I want to have this result:

p_id      Day Difference
15        6 Days
16        10 Days
17        4 Days

Do you have any offer that can generate this result in sql statement?

Answer 1

This should work in general

select p_id, max(TreatmentDate) - min(TreatmentDate) from 
patientsTable group by p_id

more specifically, for MSSQL Server

select p_id, DATEDIFF(D, MIN(TreatmentDate), MAX(TreatmentDate)) from 
patientsTable group by p_id