On 4/5/23 23:21, Louis Tian wrote:
This is a question/feature request.
Given the definition of upsert, I'd expect an upsert command to do the
following.
- `upsert into person (id, name) values (0, 'foo')` to insert a new row
- `upsert into person (id, is_active) values (0, true)` updates the is_active
column for the row inserted above
Naturally, since there isn't a real upsert command in PostgreSQL this won't
work today.
But can we achieve the same effect with "INSERT ... ON CONFLICT DO UPDATE" like
a lot of references on the internet seems to suggest.
insert into person (id, name) values (0, 'foo') on conflict ("id") do update
set id=excluded.id, name=excluded.name
insert into person (id, is_active) values (0, true) on conflict ("id") do
update set id=excluded.id, is_active=excluded.is_active
insert into person (id, name, is_active) values (0, '', true) on
conflict ("id") do update set id=excluded.id, name=person.name,
is_active=excluded.is_active ;
INSERT 0 1
select * from person;
id | name | is_active
----+------+-----------
0 | foo | t
Unfortunately. the second statement will fail due to violation of the not null constraint
on the "name" column.
PostgreSQL will always try to insert the row into the table first. and only
fallback to update when the uniqueness constraint is violated.
Is this behavior wrong? maybe not, I think it is doing what it reads quite
literally.
That being said, I have never had a need for the ON CONFLICT DO UPDATE
statement other than where I need upsert.
But using it as "upsert" is only valid when the table is absent of any NOT NULL
constraint on it's non primary key columns.
So, if my experience/use case is typical (meaning the main purpose / use case
for ON CONFLICT DO UPDATE is to support upsert) then it can be argue the
current behavior is incorrect?
This has been a source confusion to say at least.
https://stackoverflow.com/questions/48816629/on-conflict-do-nothing-in-postgres-with-a-not-null-constraint
https://www.postgresql.org/message-id/flat/1996438.1604952901%40sss.pgh.pa.us#ace8adc1354265aca5672028faea0c0f
The MERGE command introduced in PG15 in theory can be used to do UPSERT
properly that is void of the aforementioned limitation.
The downside is it is rather verbose.
*Question*
This there a way to do an upsert proper prior to PG15?
*Feature Request*
Given that UPSERT is an *idempotent* operator it is extremely useful.
Would love to see an UPSERT command in PostgreSQL so one can 'upsert' properly
and easily.
Regards,
Louis Tian
--
Adrian Klaver
[email protected]
