Changed a column type from "integer" to varchar

Hello,

You can not currently change the data type with alter table.

J

Ying Lu wrote:

Hi,

I have a question about alter a column's type in a postgreSQL table.

For example, I have 10, 000 records in a table name "test", I'd like to
change column "machineID" type from integer to varchar. I am looking for
something like:

alter table test alter column machineID ... ... varchar

Thanks in advance,

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Hi,

If you're using 7.4 or below (I'm not sure if 7.5 is able to do this),
you'll end up writing the data first to a temporary table, as in (for
example):

SELECT * INTO TEMPORARY MyTable
FROM yourtable;

DROP TABLE yourtable;

CREATE TABLE yourtable (
/* with varchar stuff */
) WITH OIDS;

INSERT into yourtable
(
your field list
)
SELECT
cast(anumber as varchar(20)),
etc,
from MyTable;

Drop MyTable;

Regards,

Arthur

On Tue, Sep 14, 2004 at 01:33:32PM -0700, Joshua D. Drake wrote:

You can not currently change the data type with alter table.

... but you can add a new column with the desired type, UPDATE it with
the transformed data, and the DROP the old column.

Ying Lu wrote:

I have a question about alter a column's type in a postgreSQL table.

For example, I have 10, 000 records in a table name "test", I'd like to
change column "machineID" type from integer to varchar. I am looking for
something like:

alter table test alter column machineID ... ... varchar

--
Alvaro Herrera (<alvherre[a]dcc.uchile.cl>)
"Escucha y olvidar�s; ve y recordar�s; haz y entender�s" (Confucio)

On Tue, 14 Sep 2004 13:33:32 -0700, Joshua D. Drake
<jd@commandprompt.com> wrote:

You can not currently change the data type with alter table.

Are there any plans to add this functionality?

What's the best workaround? Add a new column, copy data from old
column to new column, drop old column?

--
Greg Donald
http://destiney.com/

On Tue, Sep 14, 2004 at 03:53:07PM -0500, Greg Donald wrote:

On Tue, 14 Sep 2004 13:33:32 -0700, Joshua D. Drake
<jd@commandprompt.com> wrote:

You can not currently change the data type with alter table.

Are there any plans to add this functionality?

It's in 8.0 already.

--
Alvaro Herrera (<alvherre[a]dcc.uchile.cl>)
"No necesitamos banderas
No reconocemos fronteras" (Jorge Gonz�lez)

Currently, what I did is like

. alter table test add column machineIDnew varchar;
. update test set machineIDnew = machineID;
. alter table test rename machineIDnew to machineID;
. vacuum full table;

If better ways, please let me know.

Thanks a lot,

Greg Donald wrote: