DataTypeDescriptor(DTD) needs to have collation type and collation derivation.
These new fields will apply only for character string types. Other types should
ignore them.
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Key: DERBY-2524
URL: https://issues.apache.org/jira/browse/DERBY-2524
Project: Derby
Issue Type: New Feature
Components: SQL
Affects Versions: 10.3.0.0
Reporter: Mamta A. Satoor
Assigned To: Mamta A. Satoor
This the one of the ground works for getting different kinds of collations
working for character string types. More information on this project can be
found at
http://wiki.apache.org/db-derby/BuiltInLanguageBasedOrderingDERBY-1478.
Basically, all the types in Derby have a DTD associated with them. For
character string types, these DTDs should have valid values for collation
derivation and collation type. For other data types, these 2 fields do not
apply and should be ignored.
SQL spec talks about character string types having collation type and collation
derivation associated with them (SQL spec Section 4.2.2 Comparison of character
strings). If collation derivation says explicit or implicit, then it means that
there is a valid collation type associated with the charcter string type. If
the collation derivation is none, then it means that collation type can't be
established for the character string type.
1)Collation derivation will be explicit if COLLATE clause has been used for
character string type (this is not a possibility for Derby 10.3, because we are
not planning to support SQL COLLATE clause in this release).
2)Collation derivation will be implicit if the collation can be determined w/o
the COLLATE clause eg CREATE TABLE t1(c11 char(4)) then c11 will have collation
of USER character set. Another eg, TRIM(c11) then the result character string
of TRIM operation will have collation of the operand, c11.
3)Collation derivation will be none if the aggregate methods are dealing with
character strings with different collations (Section 9.3 Data types of results
of aggregations Syntax Rule 3aii).
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