如何在 Postgresql 中创建具有固定日期 + 随机时间间隔的复合日期时间

Question

I'm new to Postgresql, and I'm looking for a way to return a composite datetime, built with a fixed date, and a random time, defined as an interval.

An example:

2020-12-02 10:00:00
2020-12-02 10:10:20
2020-12-02 08:25:23
2020-12-02 09:12:11

As you can see the date is fixed, and time remains between 08:00:00 and 10:30:00.

Do you know how to replicate this behaviour using a Postgresql query?

Answer 1

As a total newbie of Postgresql (but with some experience in general SQL), and reading some posts here, I've found an easy way to get it done:

SELECT

 CURRENT_DATE + time '08:00:00' + 

 (random() * interval '3 hours')::time

AS date_wrandom_t

FROM generate_series(1, 50)

generate_series its here only to demonstrate some results, you can omit it and get a single result.

What it does:

1. Takes the current date (today)
2. Defines the starting time (min value)
3. Generate a random interval of 3 hours - (tested with SELECT (random() * interval '3 hours')::time )
4. Add the result to the minimum time (08:00:00)

Maybe it's not the best solution, but I like it as it's based on a simple syntax, easy to remember.

I wish to find some time to study this DBMS, it seems really powerful.

Any addition/suggestion is welcome!

Answer 2

I would suggest:

select '2020-12-02 08:00:00'::timestamp + random() * interval '2 hour 30 minute'

Or, for the current date, you could express this as:

select current_date + interval '08:00:00' + random() * interval '02:30'

Note that these illustrate two different ways of expressing an interval with 2 hours and 30 minutes (and not even giving interval '150 minute' as an example).