From: | Scott Marlowe <scott(dot)marlowe(at)gmail(dot)com> |
---|---|
To: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
Cc: | jd(at)commandprompt(dot)com, Richard Huxton <dev(at)archonet(dot)com>, rod(at)iol(dot)ie, Christine Penner <christine(at)ingenioussoftware(dot)com>, Bill Moran <wmoran(at)potentialtech(dot)com>, Postgres-General <pgsql-general(at)postgresql(dot)org> |
Subject: | Re: Cast char to number |
Date: | 2010-02-24 20:46:37 |
Message-ID: | dcc563d11002241246x34979903j49054b5f43e3f833@mail.gmail.com |
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Lists: | pgsql-general |
On Wed, Feb 24, 2010 at 1:43 PM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
> "Joshua D. Drake" <jd(at)commandprompt(dot)com> writes:
>> On Wed, 2010-02-24 at 20:22 +0000, Richard Huxton wrote:
>>> ALTER TABLE t ALTER COLUMN c TYPE integer USING c::integer;
>
>> That won't work in this case. char() can't be cast to int/numeric. Not
>> only that it isn't possible to clean up the data in table because char
>> automatically pads.
>
>> postgres=# alter table foo alter column id type numeric;
>> ERROR: column "id" cannot be cast to type "pg_catalog.numeric"
>
> That just indicates that there isn't an *implicit* coercion from char to
> numeric. With a USING clause you can specify an arbitrary conversion.
>
> I agree with the recommendation to test it out before actually doing
> the table change though. Maybe look at the results of
>
> select id, id::numeric from your_table
>
> to see if it looks sane for all the different data formats in the
> column.
And if the database is mostly sitting idle (i.e. no other users) you
can always just do
begin;
alter table yada;
test how it went and then commit or rollback.
For the OP: It's a bad idea to do that kind of stuff in production
cause you'll put a lock on the table others will have to wait for.
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