Thread: Adding a NOT NULL column?

So I can add a column like:

  ALTER TABLE t ADD c SMALLINT

and I can then set it's default value like:

  ALTER TABLE t ALTER c SET DEFAULT 0

but how do set that new column to be NOT NULL?  The postgres docs say
do something like:

  ALTER TABLE t ADD (table constraint definition)

so I would do that like:

  ALTER TABLE ADD c NOT NULL
  ALTER TABLE ADD CONSTRAINT c NOT NULL

each time it fails on the 'NOT'.  How do I add that constraint?

* Philip Molter
* DataFoundry.net
* http://www.datafoundry.net/
* philip@datafoundry.net

> but how do set that new column to be NOT NULL?  The postgres docs say
> do something like:
>
>   ALTER TABLE t ADD (table constraint definition)
>
> so I would do that like:
>
>   ALTER TABLE ADD c NOT NULL
>   ALTER TABLE ADD CONSTRAINT c NOT NULL
>
> each time it fails on the 'NOT'.  How do I add that constraint?

I believe you can either ALTER the column (much like you did when you added
the default value: ALTER TABLE t ALTER c SET DEFAULT 0), or ADD a CHECK
constraint which checks that 'c IS NOT NULL'. I don't think you can simply
*add* a 'NOT NULL' constraint to a column after the fact.

Both of these should work fine, although I'm more comfortable with the
syntax of the first:

ALTER TABLE ALTER COLUMN c NOT NULL;
-OR-
ALTER TABLE ADD CONSTRAINT CHECK (c IS NOT NULL);

Greg

i've always had to add the column first and then do:

update pg_attribute set attnotnull = 't' where attname = 'fieldname' and
attrelid = (select oid from pg_class where relname = 'tablename');

but i'm using version 7.0.2, maybe the alter column to set not null works in
later versions?

tamsin

-----Original Message-----
From: pgsql-general-owner@postgresql.org
[mailto:pgsql-general-owner@postgresql.org]On Behalf Of Gregory Wood
Sent: 26 June 2001 20:11
To: Philip Molter
Cc: PostgreSQL-General
Subject: [GENERAL] Re: Adding a NOT NULL column?


> but how do set that new column to be NOT NULL?  The postgres docs say
> do something like:
>
>   ALTER TABLE t ADD (table constraint definition)
>
> so I would do that like:
>
>   ALTER TABLE ADD c NOT NULL
>   ALTER TABLE ADD CONSTRAINT c NOT NULL
>
> each time it fails on the 'NOT'.  How do I add that constraint?

I believe you can either ALTER the column (much like you did when you added
the default value: ALTER TABLE t ALTER c SET DEFAULT 0), or ADD a CHECK
constraint which checks that 'c IS NOT NULL'. I don't think you can simply
*add* a 'NOT NULL' constraint to a column after the fact.

Both of these should work fine, although I'm more comfortable with the
syntax of the first:

ALTER TABLE ALTER COLUMN c NOT NULL;
-OR-
ALTER TABLE ADD CONSTRAINT CHECK (c IS NOT NULL);

Greg


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