Thread

1. some info about char(1)

   And. Andruikhanov <andy@euinf.dp.ua> — 2001-02-01T16:49:53Z

   Good day.
   
   It's some differences in results, then I inserted char(1) type:
   
   create table ku(n_pp int4, col char(1));
   
   insert into ku values(1, '\000');
   insert into ku values(2, '\040');
   insert into ku values(3, ichar(0));
   insert into ku values(4, ichar(32));
   
   select n_pp, ascii(col) from ku ;
    n_pp | ascii 
   ------+-------
       1 |    32 
       2 |    32 
       3 |     0 
       4 |    32 
   (4 rows)      
   
   Look at the strings where n_pp equal 1 and 2. "Col" column always equals to 32
   (decimal), but I inserted as '\000' and '\040'.
     If I use ichar() function, then "col" column has another values. 
   Is it right ?
     Locales for "postgres" user adjust properly (if it's necessary).
     Postgresql version: 7.0.2 on FreeBSD 4.2-stable.
   
   ps. I use some function from list, which generated by "\df" command from psql
   console. But I didn't found them in pgsql documentation. Is it possible that
   this function will be removed in future version of postgresql ?
   pps. Can I take description of this function ?
     sorry for my bad english ;)
   
   
     Regards..
   --
   
   
   

2. insert char(1) type by different ways.

   And. Andruikhanov <andy@euinf.dp.ua> — 2001-02-02T09:30:50Z

   Good day.
   
   System Configuration                                              
   ---------------------                                             
     Architecture: Intel Pentium
   
     Operating System: 4.2-STABLE FreeBSD
                                                                     
     PostgreSQL version:   PostgreSQL-7.0.2
   
     Compiler used:  gcc 2.95.2
   
   Description of problem
   ----------------------
   
   It's some differences in results, then I inserted char(1) type. I introduce one 
   example:
   
   create table ku(n_pp int4, col char(1));
   
   insert into ku values(1, '\000');
   insert into ku values(2, '\040');
   insert into ku values(3, ichar(0));
   insert into ku values(4, ichar(32));
   
   select n_pp, ascii(col) from ku ;
    n_pp | ascii 
   ------+-------
       1 |    32 
       2 |    32 
       3 |     0 
       4 |    32 
   (4 rows)      
   
   Look at the strings where "n_pp" equal 1 and 2. "Col" column always equals to 32
   (decimal), but I inserted as '\000' and '\040'. (It is first way).
     In second way, If I use ichar() function, then "col" column has another
   values. This result is correct (I think). 
   Is it right ?
     Locales for "postgres" user adjust properly (if it's necessary).
   
   ps. I use some function from list, which generated by "\df" command from psql
   console. But I didn't found them in pgsql documentation. Is it possible that
   this function will be removed in future version of postgresql ?
   pps. Can I take description of this function ?
     sorry for my bad english ;)
   
   
     Regards..
   --
   
   
   
   

3. Re: insert char(1) type by different ways.

   Tom Lane <tgl@sss.pgh.pa.us> — 2001-02-03T20:33:52Z

   "And. Andruikhanov" <andy@euinf.dp.ua> writes:
   > insert into ku values(1, '\000');
   
   This cannot work as you expect, because what comes out of the parser is
   a string containing a single null character --- and that's fed to a
   datatype input routine that expects a null-terminated string.  So the
   char(n) input routine thinks you entered just '', which it blank-pads
   to one character.
   
   In general the Postgres I/O routines are not friendly to embedded nulls.
   The char/varchar/text types could not support embedded nulls even
   without the I/O problem, because they depend on C library routines like
   strcoll(), and those routines don't support strings with embedded nulls.
   
   			regards, tom lane
   
   

4. Re: insert char(1) type by different ways.

   Karel Zak <zakkr@zf.jcu.cz> — 2001-02-05T09:10:08Z

   On Sat, 3 Feb 2001, Tom Lane wrote:
   
   > "And. Andruikhanov" <andy@euinf.dp.ua> writes:
   > > insert into ku values(1, '\000');
   > 
   > This cannot work as you expect, because what comes out of the parser is
   > a string containing a single null character --- and that's fed to a
   > datatype input routine that expects a null-terminated string.  So the
   > char(n) input routine thinks you entered just '', which it blank-pads
   > to one character.
   > 
   > In general the Postgres I/O routines are not friendly to embedded nulls.
   > The char/varchar/text types could not support embedded nulls even
   > without the I/O problem, because they depend on C library routines like
   > strcoll(), and those routines don't support strings with embedded nulls.
   
    And how store \000 to DB to standard tuples without exotic LO?
   
    By the way, for example MySQL client lib has nice (simple) function
   that make correction from "arbitrary-data" to string that is correct
   for all MySQL FE/BE routines (function convert problematic chars to \Oct 
   format). It's good feature, because user not must yourself check all
   strings and know how chars is right for used DB.   
   
    x1 = "Boys don't cry";
   
    mysql_escape_string(x2, x1, strlen(x1));
   
    ... and x2 is "Boys don\'t cry"
   
    (I not sure if quote is good example, but for others problematic chars
   is good tool.)
   
   		Karel   
   
   
   

5. Re: some info about char(1)

   Karel Zak <zakkr@zf.jcu.cz> — 2001-02-05T16:06:16Z

   > console. But I didn't found them in pgsql documentation. Is it possible that
   > this function will be removed in future version of postgresql ?
   > pps. Can I take description of this function ?
   
    As said Tom, ichar() is chr() in 7.1. 
   
   Lates (devel) docs:
   
   http://www.postgresql.org/devel-corner/docs/user/functions-string.htm
   
   
    chr(integer) text Returns the character with the given ASCII code.
   
   		Karel