Hi Mamta,
Thanks for describing this behavior on a tidy wiki page. Having all of
this material collected in one place is great. I have a comment:
6)CHAR, VARCHAR functions do not look like they are defined in the SQL
spec. But based on 5) above, the result character string type's
collation can be considered same as the first argument's collation type
if the first argument to CHAR/VARCHAR function is a character string
type. If the first argument is not character string type, then the
result character string of CHAR/VARCHAR will have the same collation as
current schema's character set. The collation derivation will be implicit.
I think the behavior would be easier to understand if it were uniform,
that is, if the CHAR and VARCHAR operators always returned strings which
had the collation of the current schema. I suspect you will find that
this is easier to implement. I also think that this is the intention of
the SQL Standard. Here is my reasoning:
It seems to me that there is a default (implementation-defined)
character set and collation for the whole database. That default can be
overridden at the session, schema, and client-module levels. That is,
once you know what database, session, schema, and client-module you are
in, you know the default character set and collation for string
datatypes mentioned by your SQL statements. This default can be
explicitly overridden with a CAST or COLLATE clause. There are also
explicit exceptions to this behavior for certain operators (e.g., TRIM,
UPPER, LOWER, SUBSTR). The default character set and collation apply
unless the SQL Standard explicitly defines an exception or your
statement explicitly overrides the default. The default character set
and collation apply to the return types of the CHAR and VARCHAR
operators because the SQL Standard does not carve out an explicit
exception for these operators.
Is there some problem that would be solved by adopting the non-uniform
behavior proposed on the wiki page?
Thanks,
-Rick
Mamta Satoor wrote:
Hi,
I have created a wiki page for DERBY-1478 : Add built in language
based ordering and like processing to Derby
The wiki page is located at
http://wiki.apache.org/db-derby/BuiltInLanguageBasedOrderingDERBY-1478 and
it includes the current design proposal along with line items. If
anyone has any comments, please let me know.
thanks,
Mamta
