[jira] Created: (DERBY-890) Improve query processing of Derby by evaluating common sub expressions only once, rather than evaluating them many times.

["Satheesh Bandaram (JIRA)" <de...@db.apache.org>]

Improve query processing of Derby by evaluating common sub expressions only once, rather than evaluating them many times.
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         Key: DERBY-890
         URL: http://issues.apache.org/jira/browse/DERBY-890
     Project: Derby
        Type: Improvement
  Components: SQL  
    Versions: 10.2.0.0, 10.1.3.0    
 Environment: generic
    Reporter: Satheesh Bandaram


Improve Derby query processing by evaluating common sub-expressions only once. There have been discussions about common expression evaluations in DerbyDev list in the past that can be searched on for details.

Here is one example query that could benifit by this optimization. Reported by Harri Pesonen.

Select min(i) from BIG_TABLE is fast (with index on i) where as Select min(i), min(i)+1 from BIG_TABLE is slooow.

There are potentially many possible queries that could benifit by this optimization.

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