Обсуждение: Type of bare text strings

What type are bare strings considered if they haven't been cast? I'm curious as
to how the first case is of size 5, and how the last case is 301...

decibel=# select pg_column_size('test');             5

decibel=# select pg_column_size('test'::varchar);             8

decibel=# select pg_column_size('test'::text);             8

decibel=# select pg_column_size('test'::name);            64

decibel=# select pg_column_size('test'::char(4));             8

decibel=# select
pg_column_size('123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890');
         301
 

decibel=# 
-- 
Jim C. Nasby, Sr. Engineering Consultant      jnasby@pervasive.com
Pervasive Software      http://pervasive.com    work: 512-231-6117
vcard: http://jim.nasby.net/pervasive.vcf       cell: 512-569-9461

Jim C. Nasby wrote:
> What type are bare strings considered if they haven't been cast? I'm curious as
> to how the first case is of size 5, and how the last case is 301...
> 
> decibel=# select pg_column_size('test');
>               5

"unknown".  This seems to be a cstring (i.e. length 5 considering the
trailing \0)

> decibel=# select pg_column_size('test'::varchar);
>               8
> decibel=# select pg_column_size('test'::text);
>               8
> decibel=# select pg_column_size('test'::char(4));
>               8

4 fixed varlena + 4 string length

> decibel=# select pg_column_size('test'::name);
>              64

name is fixed 64 bytes (not varlena)


> decibel=# select
pg_column_size('123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890');
>             301

Same as the first case.  (There are actual 300 chars here according to
my count, is that right?)

-- 
Alvaro Herrera                                http://www.CommandPrompt.com/
The PostgreSQL Company - Command Prompt, Inc.

Alvaro Herrera wrote:
> Jim C. Nasby wrote:
> > What type are bare strings considered if they haven't been cast? I'm curious as
> > to how the first case is of size 5, and how the last case is 301...
> > 
> > decibel=# select pg_column_size('test');
> >               5
> 
> "unknown".  This seems to be a cstring (i.e. length 5 considering the
> trailing \0)

Yup.  This is handled by this code:
   else if (typlen == -2)   {       /* cstring */       result = strlen(DatumGetCString(value)) + 1;   }


-- 
Alvaro Herrera                                http://www.CommandPrompt.com/
PostgreSQL Replication, Consulting, Custom Development, 24x7 support

Alvaro Herrera <alvherre@commandprompt.com> writes:
> "unknown".  This seems to be a cstring (i.e. length 5 considering the
> trailing \0)

Yeah.  "unknown" used to have the same representation as "text", ie
varlena, but I changed it recently because I realized that the normal
thing we do with an "unknown" literal is feed it to some datatype's
input converter.  Making it the same as cstring saves a conversion step.
        regards, tom lane