Re: BUG #17258: Unexpected results in CHAR(1) data type

> On Oct 29, 2021, at 11:14 AM, PG Bug reporting form <noreply@postgresql.org> wrote:
>
> select length(substr('   '::varchar,1,1)), ascii(substr('
> '::varchar,1,1));
> produces==> 1    32   (as expected)
>
> select length(substr('   '::char,1,1)), ascii(substr('   '::char,1,1));
> produces==> 0     0     (not as expected)

There are four substr() functions defined in the standard distribution.  They are:

  substr(text, int4, int4)
  substr(text, int4)
  substr(bytea, int4, int4)
  substr(bytea, int4)

There is none defined directly for char(n).  Since "text" is the preferred type (not "bytea"), I expect a cast of your
''::char to text before entry to the function.  So the question is why casting ' '::char to text is different than '
'::text. The answer is that cast is implemented using rtrim1, which trims trailing space. 

—
Mark Dilger
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company