Обсуждение: alter table alter column to resize a varchar

Hi folks.

I'm planning on extending a field in one of my main tables using:

alter table stock alter column type varchar(255);

to extend it from the current varchar(80).  My concern is that this table and
this field is used in a number of views, and views of views.

Are then any gotchas that I need to worry about or things I need to check, or
will it just work?

Gary
--
Gary Stainburn
Group I.T. Manager
Ringways Garages
http://www.ringways.co.uk

On Thu, Sep 27, 2012 at 2:23 AM, Gary Stainburn
<gary.stainburn@ringways.co.uk> wrote:
> Hi folks.
>
> I'm planning on extending a field in one of my main tables using:
>
> alter table stock alter column type varchar(255);

Why not just do

   alter table stock alter column  type text;

That is, do you really need a limit?  The VARCHAR type in Postgress is
just a TEXT type with an additional test to limit data to 255
characters.  It doesn't save space to limit the length.

> to extend it from the current varchar(80).  My concern is that this table and
> this field is used in a number of views, and views of views.
>
> Are then any gotchas that I need to worry about or things I need to check, or
> will it just work?

You can't alter a table that has dependent views.

  => alter table foo alter t type varchar(255);
  ERROR:  cannot alter type of a column used by a view or rule
  DETAIL:  rule _RETURN on view fooview depends on column "t"

I keep scripts around to rebuild all of my views when necessary. If I
keep the scripts up to date, it make me much more willing to make a
schema change instead of putting it off until things are really messy.

Craig

On Thursday 27 September 2012 15:49:53 Craig James wrote:
> On Thu, Sep 27, 2012 at 2:23 AM, Gary Stainburn
>
> <gary.stainburn@ringways.co.uk> wrote:
> > Hi folks.
> >
> > I'm planning on extending a field in one of my main tables using:
> >
> > alter table stock alter column type varchar(255);
>
> Why not just do
>
>    alter table stock alter column  type text;
>
> That is, do you really need a limit?  The VARCHAR type in Postgress is
> just a TEXT type with an additional test to limit data to 255
> characters.  It doesn't save space to limit the length.
>

I had an arbitary limit of 80 to keep the data managable within the
applications. Now that limit is insufficient it may be worth re-evaluating
the requirement.

> > to extend it from the current varchar(80).  My concern is that this table
> > and this field is used in a number of views, and views of views.
> >
> > Are then any gotchas that I need to worry about or things I need to
> > check, or will it just work?
>
> You can't alter a table that has dependent views.
>
>   => alter table foo alter t type varchar(255);
>   ERROR:  cannot alter type of a column used by a view or rule
>   DETAIL:  rule _RETURN on view fooview depends on column "t"
>
> I keep scripts around to rebuild all of my views when necessary. If I
> keep the scripts up to date, it make me much more willing to make a
> schema change instead of putting it off until things are really messy.

I have similar scripts for most of my scripts, but wasn't sure if I'd have to
use them. Looks like I will, so I'll have to check that they're up-to-date.

Thanks for the help Craig



--
Gary Stainburn
Group I.T. Manager
Ringways Garages
http://www.ringways.co.uk