Re: Changing a table column datatype

On Tue, 2003-05-13 at 01:18, marshall(at)perilith(dot)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(dot)Elphick(at)lfix(dot)co(dot)uk
Isle of Wight, UK http://www.lfix.co.uk/oliver
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