Postgresql get rows based on minimum value

Question

Having this table:

warehouse_id	destination_id	days
1	1	2
1	1	3
2	1	3
2	1	4
3	1	5
3	2	5
1	2	2
2	2	3

I'd like to get the warehouse_id and days for each value of warehouse_id, where the row has the minimum value of days, and destination_id matches a specific value, ordered by days.

For example for destination_id = 1

warehouse_id	days
1	2
2	3
3	5

• Akina: the minimum value of days MIN() for destination_id = 1 WHERE for each value of warehouse_id GROUP BY
• Erwin Brandstetter: The best solution depends on undisclosed cardinalities. See: stackoverflow.com/a/7630564/939860, dba.stackexchange.com/a/177174/3684

Answer 1

Here is the query which orders by first for warehouse_id and days then gets first record only according to DISTINCT ON clause

select distinct on (warehouse_id) 
 warehouse_id,
 days 
 from this_table 
 where destination_id = 1 
 order by warehouse_id, days 

warehouse_id | days
-----------: | ---:
 1 | 2
 2 | 3
 3 | 5

db<>fiddle here

Answer 2

A simple aggregation like

select warehouse_id, min(days)
from this_table
where destination_id = 1
group by warehouse_id;

gives the answer in the question.