I am struggling to write a PostreSQL query. Let me explain what I'm trying to achieve:
I have two tables (lets name them A and B). I've modified table A to contain two new fields that I need to populate from B. A & B have a 1-to-many
relationship so I need to use a ORDER BY
and LIMIT 1
at the same time.
The query looks like this:
UPDATE a
SET x=b.x, y=b.y
FROM b
WHERE a.some_id=b.some_id
ORDER BY b.z ASC
LIMIT 1
and I am getting the following error:
SELECT DISTINCT ON expressions must match initial ORDER BY expressions
Any help would be greatly appreciated! Thanks in advance
CodePudding user response:
You need a subquery that picks the latest row from b
for each a
UPDATE a
SET x=b.x, y=b.y
FROM (
select distinct on (b.some_id) *
from b
order by some_id, some_timestamp desc --<< picks the latest
) b
WHERE a.some_id = b.some_id