db-derby-dev mailing list archives

Site index · List index
Message view « Date » · « Thread »
Top « Date » · « Thread »
From "Mamta Satoor" <msat...@gmail.com>
Subject Re: Collation and parameter markers (?)
Date Wed, 06 Jun 2007 13:35:09 GMT
Dan and Mike asked
"Not sure where this UCS_BASIC is coming from, can you explain?"

For the CHAR(10) part of the CAST(name as CHAR(10)) expression, sqlgrammar's
dataTypeCommon method calls characterStringType() which makes following call
to generate DTD for character string type

DataTypeDescriptor.getBuiltInDataTypeDescriptor(type, length)
Note that this method has no info about collation type and hence we end up
generating a DTD with default value of UCS_BASIC for collation type and
IMPLICIT for collation derivation(these default values are in
TypeDescriptorImpl lines 58 and 60). Next, when CastNode.init method is
called, it gets the CAST target as a DTD with collation type of UCS_BASIC
and collation derivation of IMPLICIT. Later at bind time of CastNode, it's
bindCastNodeOnly() method gets called which sets the DTD of the result of
the CAST to the same value as the DTD fro the CAST target and hence it ends
up having collation type of UCS_BASIC. The call in bindCastNodeOnly() looks
as follows
  setType(castTarget);


Mamta



On 6/5/07, Daniel John Debrunner <djd@apache.org> wrote:
>
> Mamta Satoor wrote:
> > OK, so I need to admit that my head is spinning with all these different
> > collation rules. Mike I think you are right that the result of the CAST
> > should pick the collation of the cast operand as mentioned in rule #4 on
> > wiki. I will go ahead and fix the CAST code to pick up it's collation
> > from it's operand.
>
> That's not what Mike says, or the wiki page says. Mike wrote, which
> matches the wiki page:
> > > That this would mean the cast would pick up the collation of the
> >>     compile
> >>     schema, which I assume in the example is user.
>
>
> > So, going back to my original mail earlier, I think with the current
> > code of char(10) always taking UCS_BASIC collation, we still have the
> > problem that CAST(? as char(10)) will always return UCS_BASIC and hence
> > we can't compare such a CAST with persistent character column from a
> > user table.
>
> Not sure where this UCS_BASIC is coming from, can you explain?
>
> Dan.
> >
> >  > Consider following case for parameter with CAST.
> >  > select * from customer where CAST(? as char(10)) = name
> >  > The CAST node will assign the DTD associated with char(10) to the ?.
> But
> >  > what should be the collation type for char(10). Currently in the
> code,
> >  > it is UCS_BASIC and hence ? ends up getting UCS_BASIC. As a result,
> the
> >  > result of the CAST operand gets a collation type of UCS_BASIC amd the
> >  > comparison against "name" fails with compilation time error. Now
> doing a
> >  > CAST on "name" is not an option to fix this problem because CAST(name
> as
> >  > char(10)) will result in a character string type with collation of
> >  > territory based. So, the question is what should be the collation
> type
> >  > of char(10) in the eg above?
> >
> >
> > On 6/5/07, *Mike Matrigali* <mikem_app@sbcglobal.net
> > <mailto:mikem_app@sbcglobal.net>> wrote:
> >
> >
> >
> >     Mamta Satoor wrote:
> >      > you are right. Both the sides have the same collation which is
> >     UCS_BASIC
> >      > since result of CAST picks up the DTD associated with what the
> >     operand
> >      > is getting CASTed to. Since char(10) has collation type of
> UCS_BASIC
> >      > attached to it, the result of CAST picks up that collation
> >     irrespective
> >      > of collation of the operand.  I am wondering though if that is
> >     what user
> >      > would expect when writing a query like following
> >      > select * from customer where CAST(? as char(10)) = cast(name as
> >     char(10)).
> >      > That is UCS_BASIC getting used for comparison rather than
> territory
> >      > based collation.
> >      >
> >     Can you explain why cast(name as char(10)) becomes USC_BASIC?
> >
> >     I would have thought from #4 on wiki:
> >     4)<cast specification> Section 6.12 Syntax Rule 10 says that if the
> >     target data type of CAST is character string type, then collation
> type
> >     of result character string of CAST specification is the collation of
> >     the
> >     character set of the target data type. Based on 3) above, that will
> be
> >     the collation of the current schema's character set. The collation
> >     derivation will be implicit.
> >
> >     That this would mean the cast would pick up the collation of the
> >     compile
> >     schema, which I assume in the example is user.
> >
> >     as a naive user I would either expect the cast to inherit the
> implicit
> >     collation of the target of the cast, or the collation of the schema.
> >     Not sure with USC_BASIC came from.
> >
>
>

Mime
View raw message