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Subject: changing the size of a column without dump/restore
Date: Mon, 25 Nov 2002 13:57:28 -0500 (EST)
From: "Michael Richards" <michael@fastmail.ca>
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I've got a huge database table and I need to increase the size of a 
varchar from like 100 to 200 characters. As I recall the size is just 
a restriction and doesn't actually affect the format of the table 
file. 

Rather than dumping/restoring a 5Gb table with 20,000,000 rows which 
will take all day and night, is there anything I can twiddle in the 
system tables to change this size? I'd of course be backing up the 
data just in case!

-Michael
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Date: Mon, 25 Nov 2002 12:17:17 -0700
From: Roberto Mello <rmello@cc.usu.edu>
To: Michael Richards <michael@fastmail.ca>
Cc: pgsql-sql@postgresql.org
Subject: Re: changing the size of a column without dump/restore
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On Mon, Nov 25, 2002 at 01:57:28PM -0500, Michael Richards wrote:
> I've got a huge database table and I need to increase the size of a 
> varchar from like 100 to 200 characters. As I recall the size is just 
> a restriction and doesn't actually affect the format of the table 
> file. 
> 
> Rather than dumping/restoring a 5Gb table with 20,000,000 rows which 
> will take all day and night, is there anything I can twiddle in the 
> system tables to change this size? I'd of course be backing up the 
> data just in case!

PG doesn't have an 'alter table' to increase the column size of a varchar. 
But you can accomplish it by manipulating the system tables directly. The size
of a varchar is stored in pg_attribute as the actual size + 4.

For example to change a column "foo" in table "bar" to 200:

update pg_attribute 
   set atttypmod = 204 
 where attrelid = ( select oid 
                      from pg_class 
                     where relname = 'bar' ) 
and attname = 'foo';

-Roberto

P.S: I don't know if this has any bad side effects.

-Roberto

-- 
+----|        Roberto Mello   -    http://www.brasileiro.net/  |------+
+       Computer Science Graduate Student, Utah State University      +
+       USU Free Software & GNU/Linux Club - http://fslc.usu.edu/     +
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