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Date: Fri, 28 Sep 2012 15:55:09 +1100 (NCT)
From: "Mamta A. Satoor (JIRA)" <jira@apache.org>
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Subject: [jira] [Updated] (DERBY-5142) Optimizer uses table scan when it
 could use index when multiple OR clauses
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     [ https://issues.apache.org/jira/browse/DERBY-5142?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Mamta A. Satoor updated DERBY-5142:
-----------------------------------

    Urgency: Normal
    
> Optimizer uses table scan when it could use index when multiple OR clauses
> --------------------------------------------------------------------------
>
>                 Key: DERBY-5142
>                 URL: https://issues.apache.org/jira/browse/DERBY-5142
>             Project: Derby
>          Issue Type: Improvement
>          Components: SQL, Store
>            Reporter: Karl Wright
>         Attachments: repro5142.diff
>
>
> The Derby optimizer doesn't seem to recognize that a query like this:
> SELECT id,distance,linktype FROM hopcount WHERE (jobid=? AND linktype=? AND parentidhash=?) OR (jobid=? AND linktype=? AND parentidhash=?)
> ... might be best planned by using an index declared on hopcount as (jobid,linktype,parentidhash).  Instead, a table scan is always used, no matter how big the table.  Other databases have no trouble with constructs like this.
> This is a very common situation, and blocks Apache ManifoldCF from using Derby as its primary database choice.
> I've verified that the index IS successfully used with the same table statistics when the query has only ONE clause, e.g.:
> SELECT id,distance,linktype FROM hopcount WHERE (jobid=? AND linktype=? AND parentidhash=?) 

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