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From Mike Matrigali <mikem_...@sbcglobal.net>
Subject Re: Collation and parameter markers (?)
Date Tue, 05 Jun 2007 21:00:14 GMT


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.


> Mamta
> 
> 
>  
> On 6/5/07, *Daniel John Debrunner* <djd@apache.org 
> <mailto:djd@apache.org>> wrote:
> 
>     Mamta Satoor wrote:
>      > I realize that we are still discussing what should be the right
>      > collation for different character string type instances, but I
>     want to
>      > put out cases which will hopefully aid in making a decision or expose
>      > different scenarios.
>      >
>      > 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?
> 
>     Why would the two casts be different here? What makes one UCS_BASIC and
>     the other territory based?
> 
>     Dan.
> 
> 

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