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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 19:10:41 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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  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. 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 pick
 ed for a character string type is explained 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. 
+ 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 gon in readExternal
and writeExternal methods of TypeDescriptor.
  
  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.
  
@@ -79, +79 @@

  
  Store changes
  
- 1)Store column level metadata for collate in Store. Store keeps a version number that describes
the strucutre of column level metadata. For existing pre-10.3 databases which get upgraded
to 10.3 and for new 10.3 databases with default collatoin(UCS_BASIC), the structure of column
level metadata will remain same as 10.2 structure of column level metadata, ie they will not
include collate information in their store metadata. A new version would be used in Store
for structure of column level metadata if the newly created 10.3 database has asked for territory
based collation. In other words, information about collate will be kept in Store column level
metadata only if we are working with a 10.3 newly created database with territory based collation.
This approach will make sure that we do not have to do an on-disk store metadata upgrade when
upgrading a pre-10.3 database to 10.3 version.
+ 1)Store column level metadata for collate in Store. Store keeps a version number that describes
the structure of column level metadata. For existing pre-10.3 databases which get upgraded
to 10.3 and for new 10.3 databases with default collatoin(UCS_BASIC), the structure of column
level metadata will remain same as 10.2 structure of column level metadata, ie they will not
include collate information in their store metadata. A new version would be used in Store
for structure of column level metadata if the newly created 10.3 database has asked for territory
based collation. In other words, information about collate will be kept in Store column level
metadata only if we are working with a 10.3 newly created database with territory based collation.
This approach will make sure that we do not have to do an on-disk store metadata upgrade when
upgrading a pre-10.3 database to 10.3 version.
  
  2)Currently, store uses Monitor to create DVD template rows. The logic of creating DVDs
using formatids should be factored out from Monitor into DataValueFactory. Talking in terms
of code, RowUtil.newClassInfoTemplate should call DVF.classFromIdentifier rather than Monitor.classFromIdentifier.
  

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