Question

I have a PostgreSQL database with events. Each event has a datetime or an interval. Common data are stored in the events table and dates are stored in either events_dates (datetime field) or events_intervals (starts_date, ends_date both are date fields).

Sample datetime events

• I was born on 1930-06-09
• I got my driver’s license on 1950-07-12
• Christmas is on 1900-12-24 (1900 is reserved for yearly reoccuring events)

Sample interval events

• I’ll be on vacation from 2011-06-09 till 2011-07-23

Now I have a user that will want to look up these events. They will be able to fill out a form with from and to fields and in those fields they can enter full date, day, month, year, day and month, day and year, month and year in one or both fields.

Sample queries

• From May 3 to 2012 December 21 will look for events between May 3 and December 21 whose max year is 2012
• From day 3 to day 15 will look for events between the 3rd and 15th day of every month and year
• From day 3 will look for events on the 3rd day of every month and year (same if from is empty and to is not)
• From May 3 to June will look for events between May 3 and last day of June of every year
• etc.

Any tips on how to write a maintanable query (it doesn’t necessarily have to be fast)?

Some things that we thought of

• write all possible from, to and day/month/year combinations – not maintable
• compare dates as strings e.g. input: ____-06-__ where _ is a wildcard – I wouldn’t have to generate all possible combinations but this doesn’t work for intervals

Answer 1

You can write maintainable queries that additionally are fast by using the pg/temporal extension:

https://github.com/jeff-davis/PostgreSQL-Temporal

create index on events using gist(period(start_date, end_date));

select *
from events
where period(start_date, end_date) @> :date;

select *
from events
where period(start_date, end_date) && period(:start, :end);

You can even use it to disallow overlaps as a table constraint:

alter table events
add constraint overlap_excl
exclude using gist(period(start_date, end_date) WITH &&);

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write all possible from, to and day/month/year combinations – not maintable

It’s actually more maintainable than you might think, e.g.:

select *
from events
join generate_series(:start_date, :end_date, :interval) as datetime
on start_date <= datetime and datetime < end_date;

But it’s much better to use the above-mentioned period type.