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From Apache Wiki <wikidi...@apache.org>
Subject [Db-derby Wiki] Update of "BuiltInLanguageBasedOrderingDERBY-1478" by MamtaSatoor
Date Mon, 02 Apr 2007 20:31:05 GMT
Dear Wiki user,

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The following page has been changed by MamtaSatoor:
http://wiki.apache.org/db-derby/BuiltInLanguageBasedOrderingDERBY-1478

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  == Outstanding items ==
  Language changes
  
- 1)The type definition of a data type is described by DTD (DataTypeDescriptor). This DTD
will have two additional attributes called collation type and collation derivation. (These
new attributes only apply to collation sensitive types, namely char datatypes. For other data
types, these attributes will be ignored.) As per SQL spec, the collation derivation can hold
3 values, "explicit", "implicit" and "none". In Derby 10.3, the collation derivation will
never be "explicit" because Derby 10.3 does not support SQL Standard's COLLATE clause. In
Derby 10.3, the collation derivation can be "implicit" or "none". If collation derivation
is "none", then it means the collation type can't be determined. This can happen when an aggregate
function is working with operands of different collation types. If the result of such an aggregate
function is character string type, then it's collation derivation will be "none", ie it can
not be determined. Other than this aggregate "none" case, the 
 collation derivation will always be "implicit" and collation type will be UCS_BASIC/TERRITORY_BASED.
Which one of the 2 collation types is picked for a character string type is explained in detail
in section "Collation Determination".
+ 1)The type definition of a data type is described by DTD (DataTypeDescriptor). This DTD
will have two additional attributes called collation type and collation derivation. DTD probably
will need getter and setter for the 2 additional attributes.(These new attributes only apply
to collation sensitive types, namely char datatypes. For other data types, these attributes
will be ignored.) As per SQL spec, the collation derivation can hold 3 values, "explicit",
"implicit" and "none". In Derby 10.3, the collation derivation will never be "explicit" because
Derby 10.3 does not support SQL Standard's COLLATE clause. In Derby 10.3, the collation derivation
can be "implicit" or "none". If collation derivation is "none", then it means the collation
type can't be determined. This can happen when an aggregate function is working with operands
of different collation types. If the result of such an aggregate function is character string
type, then it's collation derivation will be "none",
  ie it can not be determined. Other than this aggregate "none" case, the collation derivation
will always be "implicit" and collation type will be (0)UCS_BASIC/(1)TERRITORY_BASED. Which
one of the 2 collation types is picked for a character string type is explained in detail
in section "Collation Determination".
  
  2)The TypeDescriptor for character columns always has 0 for scale because scale does not
apply to character datatypes. Starting Derby 10.3, this scale field in TypeDescriptor will
be overloaded to indicate the collate type of the character. So, if user has requested for
TERRITORY_BASED collation, then the scale in TypeDescriptor for user columns(character) will
be 1(TERRITORY_BASED). The scale will be always 0(UCS_BASIC) for SYS schema character columns
and for databases with collation set to UCS_BASIC. These changes will go in readExternal and
writeExternal methods of TypeDescriptor. Using the value 0 for UCS_BASIC will ensure that
pre-10.3 databases with scale field as 0 in TypeDescriptor will continue to use UCS_BASIC
after upgrade to 10.3, because 0 in scale field corresponds to UCS_BASIC collation type.
  
  3)When a character column is added using CREATE TABLE/ALTER TABLE, make sure that the correct
collate type is populated in the TypeDescriptor's scale field in the SYS.SYSCOLUMNS table.
  
- 4)Store column level metadata for collate in Language Layer as well. This will happen in
DataTypeDescriptor(DTD) with the addition of int collateType field. It will be set to 0(UCS_BASIC)/1(TERRITORY_BASED)/-1(UNKNOWN).
There will be get and set methods on DTD for this new field.
+ 4)WorkHorseForCollatorDatatypes should override all the collation related methods so that
it uses the non-default Collator. All the non-default-collation-sensitive classes have an
instance of WorkHorseForCollatorDatatypes which is used to call the collation related methods.
This ensures that these collation related methods are implemented in one central place rather
than in all the collation-sensitive classes. 
  
- 5)WorkHorseForCollatorDatatypes should override all the collation related methods so that
it uses the non-default Collator. All the non-default-collation-sensitive classes have an
instance of WorkHorseForCollatorDatatypes which is used to call the collation related methods.
This ensures that these collation related methods are implemented in one central place rather
than in all the collation-sensitive classes. 
- 
- 6)At compile time, make sure that the correct character class (ex SQLChar vs CollatorSQLChar)
is generated so at run time, we do not need to check what kind of Collator object need to
be used for character types. It should be all handled correctly at the code generation time
and the appropriate runtime methods (ex like method in SQLChar vs like method in WorkHorseForCollatorDatatypes)
should get called. This is the biggest unknown to me at this point and I need to do more research.
Will appreicate very much if someone has some thoughts on this.
+ 5)At compile time, make sure that the correct character class (ex SQLChar vs CollatorSQLChar)
is generated so at run time, we do not need to check what kind of Collator object need to
be used for character types. It should be all handled correctly at the code generation time
and the appropriate runtime methods (ex like method in SQLChar vs like method in WorkHorseForCollatorDatatypes)
should get called. This is the biggest unknown to me at this point and I need to do more research.
Will appreicate very much if someone has some thoughts on this.
  
  Store changes
  

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