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From Daniel John Debrunner <...@apache.org>
Subject Collation for || (and CASE etc.) - miswording in wiki page
Date Tue, 28 Aug 2007 00:04:16 GMT

The collation wiki page has this for its "rule 11":

http://wiki.apache.org/db-derby/BuiltInLanguageBasedOrderingDERBY-1478
-------------------------------------------------------------------
11)Aggregate operators involving all character string type 
operands(Concatenation (see 6.28SR5b), CASE, NULLIF, COALESCE) will 
follow SQL spec Section 9.3 Data types of results of aggregations. In 
other words, if all the operands have the same collation associated with 
them, then the collation of result character string type will be same 
and the collation derivation will be implicit. But if operands of 
different collation types are involved, then the result character string 
type will have collation derivation of none.
-------------------------------------------------------------------

The text above starting with "In other words, ..." doesn't exactly match 
the definition in the SQL standard 9.3, which is what it is trying to 
paraphrase. SQL standard says if every type has implicit derivation 
*and* is of the same type, then the collation will be of that type with 
derivation implicit, otherwise the derivation will be none.

I haven't looked at the code to see what is done in Derby, but wanted to 
throw this out as a potential issue, either the code should be fixed if 
wrong, or the wiki page clarified.

Dan.
[this is of course ignoring explicit derivation which is not yet supported].



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