PostgreSQL return exact or closest date to queried date

Question

I have the following postgresql syntax that returns values WHERE session_date matches $date_string

Problem is that sometimes the $date_string will not be available in th

Answer 1

If you want the closest date before, do it this way:

SELECT year, session_date
FROM calendar_dates
WHERE session_date < '$date_string'
ORDER BY session_date DESC
LIMIT 1;

The closest date after uses similar logic.

For the closest on either side:

SELECT year, session_date
FROM calendar_dates
ORDER BY abs(session_date - date '$date_string') 
LIMIT 1;