From: PG Bug reporting form <noreply@postgresql.org>
To: pgsql-bugs@lists.postgresql.org
Cc: james.inform@pharmapp.de
Subject: BUG #18060: Left joining rows using random() function in join condition doesn't work as expected.
Date: Fri, 18 Aug 2023 09:30:51 +0000
Message-ID: <18060-e59408b5655979ed@postgresql.org> (raw)
The following bug has been logged on the website:
Bug reference: 18060
Logged by: James Inform
Email address: james.inform@pharmapp.de
PostgreSQL version: 15.4
Operating system: Linux and Mac
Description:
/*
PostgreSQL 14.9 / 15.4 on Linux and Mac
Left joining rows using random() function in join condition
doesn't work as expected.
I have encountered this while I was trying randomly left join a record
of a source table
with exactly with one record of a link table.
Just execute the create statements under 1.
Then execute the select under 2. multiple times and watch thee
results.
*/
-- 1. Generate two tables (source and link) with 1000 rows having gapless
ids
create temp table source as
select source_id, 'source' as source_name from generate_series(1,1000) as
source_id
;
create temp table link as
select link_id, 'link' as link_name from generate_series(1,1000) as
link_id
;
-- 2. Execute this query multiple time and you will see results where:
-- * no rows from link are joined
-- * extactly one row is joined
-- * multiple rows are joined
select * from source left join link on link_id = 1 + (random()*500)::int8
order by 1
/*
I would expect always exactly one row to be joined.
Instead I get 1, none or multiple.
Is this an error or am I doing something wrong?
*/
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To: pgsql-bugs@postgresql.org
Cc: noreply@postgresql.org, pgsql-bugs@lists.postgresql.org, james.inform@pharmapp.de
Subject: Re: BUG #18060: Left joining rows using random() function in join condition doesn't work as expected.
In-Reply-To: <18060-e59408b5655979ed@postgresql.org>
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