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
aklaver@comcast.net
