Re: multicolumn partitioning help

On Sun, 2023-03-12 at 13:59 -0400, James Robertson wrote:
> I am having issues with multicolumn partitioning. For reference I am using the following link as my guide:
> https://www.postgresql.org/docs/devel/sql-createtable.html
>
> To demonstrate my problem, I created a simple table called humans. I want to partition by the year
> of the human birth and then the first character of the hash. So for each year I'll have year*16 partitions. (hex)
>
> CREATE TABLE humans (
>     hash bytea,
>     fname text,
>     dob date
>     )PARTITION BY RANGE (EXTRACT(YEAR FROM dob),substring(hash::text, 1, 1));
>    
> Reading the documentation:   "When creating a range partition, the lower bound specified with
> FROM is an inclusive bound, whereas the upper bound specified with TO is an exclusive bound".
>
> However I can't insert any of the following after the first one, because it says it overlaps.
> Do I need to do anything different when defining multi-column partitions?
>
>
> This works:
> CREATE TABLE humans_1968_0 PARTITION OF humans FOR VALUES FROM (1968, '0') TO (1969, '1');
>
>
> These fail: 
> CREATE TABLE humans_1968_1 PARTITION OF humans FOR VALUES FROM (1968, '1') TO (1969, '2');

Justin has explained what the problem is, let me supply a solution.

I think you want subpartitioning, like

CREATE TABLE humans (
hash bytea,
fname text,
dob date
) PARTITION BY LIST (EXTRACT (YEAR FROM dob));

CREATE TABLE humans_2002
PARTITION OF humans FOR VALUES IN (2002)
PARTITION BY HASH (hash);

CREATE TABLE humans_2002_0
PARTITION OF humans_2002 FOR VALUES WITH (MODULUS 26, REMAINDER 0);

[...]

CREATE TABLE humans_2002_25
PARTITION OF humans_2002 FOR VALUES WITH (MODULUS 26, REMAINDER 25);

and so on for the other years.

Yours,
Laurenz Albe