Postgresql difference between two columns dates?

Question

Username    DateStart  DateFinish
James       2017-07-01 2017-09-14
Luigi       2017-08-02 2017-09-18
Francesco   2017-09-03 2017-10-25  

How calculate with sql difference between two date columns in days?

Answer 1

You can simply subtract them like

select "DateFinish"::date - "DateStart"::date;

And if the dates column are of datatype date then you can simply do:

select "DateFinish" - "DateStart"