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 calcu

Answer 1

Try this. It extracts the number of days between 2 dates and creates a column called "days":

select extract(day from DateFinish - DateStart) as days from MyTable;