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From "Daniel John Debrunner (JIRA)" <j...@apache.org>
Subject [jira] Commented: (DERBY-3854) Implement LIKE transformations and optimizations for databases using territory-based collations
Date Fri, 29 Aug 2008 17:49:44 GMT

    [ https://issues.apache.org/jira/browse/DERBY-3854?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12627048#action_12627048
] 

Daniel John Debrunner commented on DERBY-3854:
----------------------------------------------

> (1) all the characters before the wildcard map to exactly one collation element,

Need to add 'each' at the end, right, just to be clear?

Though I maybe having trouble understanding what this is trying to say exactly. All single
characters will map to a single collation element by themselves, so I think it's really trying
to say that none of the sequence of characters in the prefix combine into a single collation
element.???

> col < 'abcde\uFFFF'

\uFFFF is incorrect since it is not a valid character and the numeric codepoint of the character
is not what the index is using for ordering. You really need

  col < 'abcdf'

where 'f' is the character determined from a collation element value than is greater than
the one for 'e'


> Implement LIKE transformations and optimizations for databases using territory-based
collations
> -----------------------------------------------------------------------------------------------
>
>                 Key: DERBY-3854
>                 URL: https://issues.apache.org/jira/browse/DERBY-3854
>             Project: Derby
>          Issue Type: Improvement
>    Affects Versions: 10.3.3.0, 10.4.1.3, 10.5.0.0
>            Reporter: Rick Hillegas
>
> The LIKE transformations and optimizations are disabled when using a database with a
territory-based collation. See the following email thread: http://www.nabble.com/territory-based-collations-and-optimizations-for-the-LIKE-operator-td19111725.html#a19111725
That thread, in turn, refers to DERBY-1478. It would be nice if we did not have to perform
full table scans for LIKE queries in databases with territory-based collations.

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