Dynamic (Column Based) Interval - postgresql

Question

How do I add a dynamic (column based) number of days to NOW?
SELECT NOW() + INTERVAL a.number_of_days "DAYS" AS "The Future Date"
FROM a;
Where a.number_of_days is an integer?

Answer 1

I usually multiply the number by interval '1 day' or similar, e.g.:
select now() + interval '1 day' * a.number_of_days from a;

Answer 2

I know this is a year old, but if you need to use a column to specify the actual interval (e.g. 'days', 'months', then it is worth knowing that you can also CAST your string to an Interval, giving:
SELECT now()+ CAST(the_duration||' '||the_interval AS Interval)
So the the original question would become:
SELECT now() + CAST(a.number_of_days||" DAYS" AS Interval) as "The Future Date" FROM a;

Answer 3

I prefer this way. I think its pretty easy and clean.
In Postgres you need interval to use + operator with timestamp
select (3||' seconds')::interval;
select now()+ (10||' seconds')::interval,now();
where you can use seconds, minutes, days, months...
and you can replace the numbers to your column.
select now()+ (column_name||' seconds')::interval,now()
from your_table;

Answer 4

Use make_interval()
SELECT NOW() + make_interval(days => a.number_of_days) AS "The Future Date"
FROM a;
But in general it might be a better idea to use a column defined as interval, then you can use any unit you want when you store a value in there.

Answer 5

To creating intervals those based on column values, I recommend to add two columns in your table. For example, column "period_value"::INT4 and column "period_name"::VARCHAR.
Column "period_name" can store the following values:
microsecond
milliseconds
second
minute
hour
day
week
month
quarter
year
decade
century
millennium
+--------------+-------------+
| period_value | period_name |
+--------------+-------------+
| 2 | minute |
+--------------+-------------+
Now you can write:
SELECT NOW() - (period_value::TEXT || ' ' || period_name::TEXT)::INTERVAL FROM table;

Answer 6

If we have field with interval string value such as '41 years 11 mons 4 days' and want to convert it to date of birth use this query :
UPDATE "february14" set dob = date '2014/02/01' - (patient_age::INTERVAL)
dob is date field to convert '41 years 11 mons 4 days' to '1972/10/14' for example
patient_age is varchar field that have string like '41 years 11 mons 4 days'
And this is query to convert age back to date of birth
SELECT now() - INTERVAL '41 years 10 mons 10 days';

Answer 7

Updating based on a column ID was a useful way to create some randomised test data for me.
update study_histories set last_seen_at = now() - interval '3 minutes' * id;