Re: Cast char to number

In response to Raymond O'Donnell <rod(at)iol(dot)ie>:

> On 24/02/2010 19:53, Christine Penner wrote:
>
> > At 11:38 AM 24/02/2010, you wrote:
> >> In response to Christine Penner <christine(at)ingenioussoftware(dot)com>:
> >>
> >> > I have a character field I want to change to a number. The values in
> >> > that field are all numbers that may or may not be padded with spaces
> >> > or 0's. What is the best way to do that?
> >>
> >> Put the values in numeric fields to begin with and cast to chars as
> >> needed. Basically reverse what you're doing.
> >
> > I don't understand what you mean. This is a column in a table that is
> > already a char and has numbers in it. I want it to be a number field not
> > character. How can I change the data type of that column without loosing
> > the data I have in it?
>
> I think what he means is that you should have been doing the reverse to
> begin with - storing numbers in the database as numeric columns, and
> then casting them to a character format as needed for display.

Actually, I misunderstood the question. I thought you were trying to
figure out how to extract the data for display. But fixing the fields
to be the right type is a noble goal :)

> However, to address your immediate problem, you could try something like
> this:
>
> (i) Create a new column of type numeric or integer as appropriate.
> (ii) update your_table set new_column = CAST(trim(both ' 0' from
> old_column) as numeric)
> (iii) Drop the old column, as well as any constraints depending on it.
> (iv) Rename the new column to the same name as the old column
> (v) Recreate any of the constraints dropped in step (iii).
>
> I think the cast in step (ii) might not be necessary - not sure about this.

Agreed. There's a slightly shorter way, you can do:
ALTER TABLE tablename ALTER COLUMN columnname TYPE INT;

If that doesn't work because the cast isn't automatic, you can add a
USING clause:

ALTER TABLE tablename
ALTER COLUMN columnname TYPE INT USING columnname::INT;

(as an example, the using clause may need to be more complicate than that).

--
Bill Moran
http://www.potentialtech.com
http://people.collaborativefusion.com/~wmoran/