Re: [GENERAL] Automatic truncation of character values & casting to the type of a column type
On Wednesday 16 December 2009 5:05:19 pm Justin Bailey wrote:
> Greetings! I am trying to avoid the old problem of inserting a 40
> character string into a 20 character field. However, I'd like to avoid
> hard-coding the acceptable length (20). Is there a way to say "cast to
> the same type as a given column"? E.g., if I have tables Long and
> Short:
>
> CREATE TABLE Long (longCol varchar(40) )
> CREATE TABLE Short (shortCol varchar(20) )
>
> And this data:
>
> INSERT INTO Long VALUES ('FOOBAR'), ('BAZ'),
> (CAST('2314J1L234J21LK342JKL32J32KL4J123LK4J13L4' AS VARCHAR(40)))
>
> Can make values inserted into shortCol have a maximum length of 20
> without hard-coding that value? Something like:
>
> INSERT INTO Short (ShortCol)
> (SELECT CAST(Long.longCol as Short.shortCol) FROM LONG)
>
> I am using postgres 8.2.
>
> Clearly this is a toy example. In the real world, I insert or update
> values in my target table using a stored procedure. I want to
> future-proof my stored procedure against the column lengths on the
> target table changing. Otherwise, I have to update my sproc with new
> lengths if the table ever changes. I have tried using the PL/PGSQL
> feature where types can be "copied" in a declaration:
>
> DECLARE
> myVal Short.shortCol%TYPE;
> ...
>
> But I can still put values which are too long into that variable, so
> it doesn't help me. Sadly, using the same syntax in a CAST fails in
> various ways:
>
> UPDATE Short SET shortCol = CAST(myVal AS Short.shortCol) -- schema
> "Short" does not exist error
> UPDATE Short SET shortCol = CAST(myVal AS Short.shortCol%TYPE) -- syntax
> error UPDATE Short SET shortCol = CAST(myVal AS (Short).shortCol) -- syntax
> error
>
> Thanks in advance for any advice.
>
> Justin
My solution would be to declare the varchar without a length restriction and
not
worry. Right off the top I see two potential problems with the truncation
procedure you are proposing. One, is if you go and reduce the field width for
the table column you will have the same truncate error. Two, what happens to
the 20 characters you are losing? They where important once are they not now?
--
Adrian Klaver
akla...@comcast.net
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Re: [GENERAL] Automatic truncation of character values & casting to the type of a column type
On Thu, Dec 17, 2009 at 10:24:28AM -0500, Tom Lane wrote: > Justin Bailey writes: > > If s was automatically truncated, the insert would succeed, but it > > fails with a "value too long" error. > > Oh, I thought the failure was the behavior you wanted. There's > no automatic truncation here --- perhaps putting an exception > block around it would be the way to go? I think the OP wants to be able to use the "%TYPE" magic in more places than the grammar currently accepts. For example, so that you can use it in a CAST expression as per some of the examples. Would using DOMAINs be a better alternative? It certainly works now. -- Sam http://samason.me.uk/ -- Sent via pgsql-general mailing list (pgsql-general@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-general
Re: [GENERAL] Automatic truncation of character values & casting to the type of a column type
Justin Bailey writes: > On Wed, Dec 16, 2009 at 7:20 PM, Tom Lane wrote: >> Really? Works for me, in everything back to 7.3. > If s was automatically truncated, the insert would succeed, but it > fails with a "value too long" error. Oh, I thought the failure was the behavior you wanted. There's no automatic truncation here --- perhaps putting an exception block around it would be the way to go? regards, tom lane -- Sent via pgsql-general mailing list (pgsql-general@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-general
Re: [GENERAL] Automatic truncation of character values & casting to the type of a column type
On Wed, Dec 16, 2009 at 7:20 PM, Tom Lane wrote:
> Really? Works for me, in everything back to 7.3.
>
I must be missing something, because this function fails:
CREATE OR REPLACE FUNCTION insertShort()
RETURNS VOID AS
$BODY$
DECLARE
s Short.shortCol%TYPE;
BEGIN
SELECT longCol INTO s FROM Long
WHERE char_length(longCol) > 20;
INSERT INTO Short (shortCol) VALUES (s);
END;
$BODY$
LANGUAGE 'plpgsql' VOLATILE;
If s was automatically truncated, the insert would succeed, but it
fails with a "value too long" error.
p.s. I used the definitions from my prior email:
CREATE TABLE Long (longCol varchar(40) );
CREATE TABLE Short (shortCol varchar(20) );
INSERT INTO Long VALUES ('FOOBAR'), ('BAZ'),
(CAST('2314J1L234J21LK342JKL32J32KL4J123LK4J13L4' AS VARCHAR(40)));
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Re: [GENERAL] Automatic truncation of character values & casting to the type of a column type
Justin Bailey writes: > I have tried using the PL/PGSQL > feature where types can be "copied" in a declaration: > DECLARE > myVal Short.shortCol%TYPE; > But I can still put values which are too long into that variable, so > it doesn't help me. Really? Works for me, in everything back to 7.3. regards, tom lane -- Sent via pgsql-general mailing list (pgsql-general@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-general
