Re: PG11 Hash partitioning and null values in the partition key

[Daniel Westermann <daniel.westermann@xxxxxxxxxxxxxxxx>]

Hi,

given this setup:

create table part2 ( a int, list varchar(10) ) partition by hash (a);

create table part2_1 partition of part2 FOR VALUES WITH (MODULUS 3, REMAINDER 0);

create table part2_2 partition of part2 FOR VALUES WITH (MODULUS 3, REMAINDER 1);

create table part2_3 partition of part2 FOR VALUES WITH (MODULUS 3, REMAINDER 2);

insert into part2 (a,list) values (1,'aaa');

insert into part2 (a,list) values (2,'bbb');

insert into part2 (a,list) values (3,'ccc');

... it is possible to insert rows like this which will always go to the first partition:

insert into part2 (a,list) values (null,'ddd');

insert into part2 (a,list) values (null,'eee');

select * from part2_1;

 a | list
---+------
 2 | bbb
   | ddd
   | eee
(3 rows)

I suppose this is intended but I could not find anything in the documentation about that. Can someone please clarify the logic behind that?

>> The calculated hash value for the null value will be zero, therefore, it will fall to the partition having remainder zero.

Thank you, Amul