Re: Changing a table column datatype

On Tue, 2003-05-13 at 01:18, marshall@perilith.com wrote:
> Hello,
>
> This has been asked before, but the responses weren't clear enough
> for me to understand.
>
> I have a table `mytable' with an attribute `mycol' of datatype char(4) and
> I'd like to change it to varchar(20).  Mycol is populated by two values -
> NULLs and four element chars.  What I've tried thusfar:
>
>  db=> ALTER TABLE mytable ADD COLUMN mycol_new VARCHAR(20);
>  ALTER TABLE
>  db=> INSERT INTO mytable (mycol_new) SELECT mycol FROM mytable;
>  ERROR:  ExecInsert: Fail to add null value in not null attribute fqdn
>
> The `fqdn' attribute is another column in mytable.
>
> So is it the case that INSERT doesn't like inserting NULL values?  Is
> there another way to do this?

INSERT inserts new rows and all constraints for the row must be
satisfied; use UPDATE to alter existing rows.

   UPDATE mytable SET mycol_new = mycol;

(no WHERE clause, because you want to change every row).
--
Oliver Elphick                                Oliver.Elphick@lfix.co.uk
Isle of Wight, UK                             http://www.lfix.co.uk/oliver
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