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https://issues.apache.org/jira/browse/CALCITE-7153?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=18017219#comment-18017219
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Julian Hyde commented on CALCITE-7153:
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We should think about this as a "wildcard token of minimum length N", and have
a normal form for such tokens. "_%_", "%__" and "%__%" are all wildcard tokens
of minimum length 2, and I propose that "__%" is the normal form.
A wildcard token is a sequence of consecutive '_' or '%' symbols. The minimum
length is the number of '_' symbols.
> Mixed wildcards of _ and % need to be simplified in LIKE operator
> -----------------------------------------------------------------
>
> Key: CALCITE-7153
> URL: https://issues.apache.org/jira/browse/CALCITE-7153
> Project: Calcite
> Issue Type: Improvement
> Components: core
> Affects Versions: 1.40.0
> Reporter: Yu Xu
> Assignee: Yu Xu
> Priority: Minor
>
> Mixed wildcards of _ and % need to be simplified in LIKE operator, such as :
>
> {code:java}
> %_%__ can be simplied to %___
> %__%__%_ can be simplied to %_____{code}
> involving % and _ can be simplified by removing all % except 1
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