Message-ID: <e506bb38aa4ac923709d075cb0e6e7710fe4c269.camel@cybertec.at>
Subject: Re: pg12 - partition by column that might have null values
From: Laurenz Albe <laurenz.albe@cybertec.at>
To: Mariel Cherkassky <mariel.cherkassky@gmail.com>,
	pgsql-performance@lists.postgresql.org
Date: Wed, 02 Oct 2019 09:29:58 +0200
In-Reply-To: 
 <CA+t6e1mnD+xP1a0kcuPMRDVUYhJu3rT9fGQ7sPe5=+d5sWykWQ@mail.gmail.com>
References: 
	<CA+t6e1mnD+xP1a0kcuPMRDVUYhJu3rT9fGQ7sPe5=+d5sWykWQ@mail.gmail.com>
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Mariel Cherkassky wrote:
> In PG12 I'm trying to create partitions by range on a date column
> that might be null (indicates it is the most recent version of the
> object). My PK has to include the partition column, therefore I'm
> getting an error that I cant create a primary key with the specific
> column because it has null values.
> 
> For example : 
> \d object_revision
>                                           Table
> "public.object_revision"
>    Column    |            Type             | Collation | Nullable |  
>                  Default
> -------------+-----------------------------+-----------+----------+
> -----------------------------------------------
>  id          | integer                     |           | not null |
> nextval('mariel_dates_test_id_seq'::regclass)
>  end_time    | timestamp without time zone |           |          |
>  object_hash | text                        |           |          |
> Indexes:
>     "id_pk" PRIMARY KEY, btree (id)
> 
> Lets say that the same object (object_hash) can have many revisions,
> the end_time is the time it was last updated. I'm trying to create
> this table as a range partition on the end_time. However, when I try
> to add the pk I'm getting an error : 
> ALTER TABLE object_revision ADD CONSTRAINT
> object_revision_id_end_time PRIMARY KEY (id,end_time);
> ERROR:  column "end_time" contains null values
> 
> does someone familiar with a workaround ? I know that in postgresql
> as part of the primary key definition unique and not null constraints
> are enforced on each column and not on both of them. However, this
> might be problematic with pg12 partitions..

Can "end_time" ever be modified?

If yes, it is a bad choice for a partitioning column.

If the NULL in "end_time" is meant to signify "no end", use the
value "infinity" instead of NULL.  Then you can define the column
as NOT NULL.

Yours,
Laurenz Albe
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