Updating another table on conflict postgres - sql

Question

I have a requirement to insert on one table (test01) and update on another table(result) whenever the conflict arises. I tried with below query:
insert into test01 as cst (col1,col2)
select col1,col2 from (
select 1 col1,'test' col2) as excluded
on conflict (col1) do
update result as rst set conflictid = excluded.col1, updated_at = now() where rst.conflictid= excluded.col1 ;
but its returns "syntax error at or near result". Can anyone please help me with the right solution.

Answer 1

Basically, your approach is not feasible. The ON CONFLICT ... DO UPDATE clause applies only to the table into which the rows are inserted. See INSERT syntax in the documentation.
A solution requires a bit more work. You should create a trigger for table test01 to get the effect you want.
Example tables (slightly changed names of columns and table):
create table test01_conflicts(
conflict_id int primary key,
updated_at timestamp);
create table test01(
id int primary key,
str text);
When the table test01 is updated with the same id the trigger function inserts or updates a row in the conflict table. Note that in this case the function returns null so the update on test01 will not proceed.
create or replace function before_update_on_test01()
returns trigger language plpgsql as $$
begin
if new.id = old.id then
insert into test01_conflicts(conflict_id, updated_at)
values (new.id, now())
on conflict(conflict_id)
do update set updated_at = now();
return null;
end if;
return new;
end $$;
create trigger before_update_on_test01
before update on test01
for each row execute procedure before_update_on_test01();
The query. On conflict update test01 with the same id only:
insert into test01
select col1, col2
from (
select 1 as col1, 'test' as col2
) as source
on conflict (id) do
update set
id = excluded.id;