Postgresql extract last row for each id
Suppose I've next data
id date another_info
1 2014-02-01 kjkj
1 2014-03-11 ajskj
1 2014-05-13 kgfd
2 2014-02-01 SADA
3 2014-02-01 sfdg
3 2014-06-12 fdsA
I want for each id extract last information:
id date another_info
1 2014-05-13 kgfd
2 2014-02-01 SADA
3 2014-06-12 fdsA
How could I manage that?
The most efficient way is to use Postgres' distinct on
operator
select distinct on (id) id, date, another_info
from the_table
order by id, date desc;
If you want a solution that works across databases (but is less efficient) you can use a window function:
select id, date, another_info
from (
select id, date, another_info,
row_number() over (partition by id order by date desc) as rn
from the_table
) t
where rn = 1
order by id;
The solution with a window function is in most cases faster than using a sub-query.
select *
from bar
where (id,date) in (select id,max(date) from bar group by id)
Tested in PostgreSQL,MySQL
I found this as the fastest solution:
SELECT t1.*
FROM yourTable t1
LEFT JOIN yourTable t2 ON t2.tag_id = t1.tag_id AND t2.value_time > t1.value_time
WHERE t2.tag_id IS NULL