Re: Cast char to number

"Joshua D. Drake" <jd@commandprompt.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