Re: Partition with check constraint with "like"

On Fri, May 21, 2021 at 02:36:14AM +0000, Nagaraj Raj wrote:
> Thank you. This is a great help. 
> But "a" have some records with alpha and numeric. 

So then you should make one or more partitions FROM ('1')TO('9').

> example :
> insert into mytable values('alpha'),('bravo');
> insert into mytable values('1lpha'),('2ravo');
>
>
> On Thursday, May 20, 2021, 06:23:14 PM PDT, David Rowley <dgrowleyml(at)gmail(dot)com> wrote:
>
> On Fri, 21 May 2021 at 12:32, Nagaraj Raj <nagaraj(dot)sf(at)yahoo(dot)com> wrote:
> > I am trying to create partitions on the table based on first letter of the column record  value using inherit relation & check constraint.
>
> You'll get much better performance out of native partitioning than you
> will with the old inheritance method of doing it.
>
> >  EXECUTE 'CREATE TABLE partition_tab.' || c_table || '(check ( name like '''|| chk_cond||''')) INHERITS (' ||TG_TABLE_NAME|| ');';
>
> This is a bad idea. There's a lock upgrade hazard here that could end
> up causing deadlocks on INSERT.  You should just create all the tables
> you need beforehand.
>
> I'd recommend you do this using RANGE partitioning. For example:
>
> create table mytable (a text not null) partition by range (a);
> create table mytable_a partition of mytable for values from ('a') to
> ('b'); -- note the upper bound of the range is non-inclusive.
> create table mytable_b partition of mytable for values from ('b') to ('c');
> insert into mytable values('alpha'),('bravo');
>
> explain select * from mytable where a = 'alpha';
>                             QUERY PLAN
> -------------------------------------------------------------------
> Seq Scan on mytable_a mytable  (cost=0.00..27.00 rows=7 width=32)
>   Filter: (a = 'alpha'::text)
> (2 rows)
>
> The mytable_b is not scanned.