To: pgsql-sql@postgresql.org
From: Jasen Betts <jasen@xnet.co.nz>
Subject: Re: Determine length of numeric field
Date: 15 Feb 2011 23:32:50 GMT
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On 2011-02-15, Tony Capobianco <tcapobianco@prospectiv.com> wrote:
> I'm altering datatypes in several tables from numeric to integer.  In
> doing so, I get the following error:
>
> dw=# \d uniq_hits
>     Table "support.uniq_hits"
>    Column   |  Type   | Modifiers 
> ------------+---------+-----------
>  sourceid   | numeric | 
>  hitdate    | date    | 
>  total      | numeric | 
>  hitdate_id | integer | 
> Indexes:
>     "uniq_hits_hitdateid_idx" btree (hitdate_id), tablespace
> "support_idx"
> Tablespace: "support"
>
> esave_dw=# alter table uniq_hits alter sourceid type int;
> ERROR:  integer out of range
>
> Sourceid should not be more than 5 digits long.  I'm able to perform
> this query on Oracle and would like something similar on postgres 8.4:
>
> delete from uniq_hits where sourceid in (select sourceid from uniq_hits
> where length(sourceid) > 5);

delete from uniq_hits where sourceid in (select sourceid from uniq_hits
where length(sourceid::text) > 5);

or even:  delete from uniq_hits where length(sourceid::text) > 5;

but using length on numbers is usually the wrong way.

do this instead:  delete from uniq_hits where abs(sourceid) > 2^32-1;
 
Which will hit all the ones that can't be converted.
 
You may want to do a select first to see what you're deleting.
 
> I haven't had much luck with the length or char_length functions on
> postgres.

The length functions only work with strings. using them on numbers is
usually the wrong thing as there is not a 1 to 1 mapping between
strings an numbers. 

Strings of length only 3 can be out of range for integer (eg: '9e9'),
(but numerics never look like that, larger floats can though)

care to guess the result of this query?

 select '9000000000000000'::float, length('9000000000000000'::float::text);

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