Postgres INTERVAL using value from table

Question

If I want to add 5 days to a date, I can do it using the INTERVAL function:

select create_ts + interval \'5 days\' from abc_company;
         


        

Answer 1

You just need a working type cast. This kind is standard SQL.

select current_timestamp + cast((num_of_days || ' days') as interval)
from abc_company;

This is an alternative syntax, peculiar to PostgreSQL.

select current_timestamp + (num_of_days || ' days')::interval
from abc_company;

I prefer not trying to remember the third kind of type cast supported by PostgreSQL, which is the function-like syntax.

select current_timestamp + "interval" (num_of_days || ' days')
from abc_company;

Why? Because some function names have to be quoted; interval is one of them.

Also, the names interval, time, and timestamp can only be used in this fashion if they are double-quoted, because of syntactic conflicts. Therefore, the use of the function-like cast syntax leads to inconsistencies and should probably be avoided.