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https://issues.apache.org/jira/browse/DERBY-4791?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12906519#action_12906519
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Bryan Pendleton commented on DERBY-4791:
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This looks like a fine approach to me. Thanks for putting the patch together.
+1.
> LIKE operator optimizations and concatenation
> ---------------------------------------------
>
> Key: DERBY-4791
> URL: https://issues.apache.org/jira/browse/DERBY-4791
> Project: Derby
> Issue Type: Improvement
> Components: SQL
> Affects Versions: 10.6.1.0
> Environment: All
> Reporter: Uriah Eisenstein
> Attachments: fold-constants.diff
>
>
> While queries of the form "<column> LIKE ' <string-constant>%' " are
> optimized into index scans, the equivalent expression using a concatenation
> "<column> LIKE ' <string-constant>' || '%' " would result in a table scan.
> Queries of the form "<column> LIKE ?" are optimizable using an internally
> generated parameter, so it doesn't seem far-fetched to generate such a
> parameter for a concatenation of strings (or other string expressions) as
> well, once its value has been calculated. This is of course limited to cases
> where the result of the string expression can be calculated once, i.e. it is
> independent of columns in the query.
> It is sometimes possible to work around this by manually adding the " x >=
> '<string-constant>' AND x < '<string-constant>\uffff...' " condition.
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