From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
---|---|
To: | jd(at)commandprompt(dot)com |
Cc: | 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 20:43:03 |
Message-ID: | 29174.1267044183@sss.pgh.pa.us |
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Lists: | pgsql-general |
"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.
regards, tom lane
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