GitHub user LosD opened a pull request:
https://github.com/apache/metamodel/pull/115
Anchor WildcardPattern to start
This makes sure the `WildcardPattern` anchors its test to the start of the
string, not only the end.
This comes with a minor performance penalty (quick test said 5-10%), but I
think correctness trumps speed here.
I would have liked to compare speed with pre-compiled regexes
(`Pattern.quote()` the operand, replace `%` with `.*?` and anchor it with `^`
and `$`), but if the LIKE operand is inside a `SelectItem`, that would mean
compiling a new regex pattern for every row, which would probably be _very_
expensive, so I opted not to try. There seem to be some similar optimization of
the IN operator, so I might be wrong, though.
Fixes METAMODEL-1103
You can merge this pull request into a Git repository by running:
$ git pull https://github.com/LosD/metamodel
METAMODEL-1103/anchor-string-start
Alternatively you can review and apply these changes as the patch at:
https://github.com/apache/metamodel/pull/115.patch
To close this pull request, make a commit to your master/trunk branch
with (at least) the following in the commit message:
This closes #115
----
commit e993e9483a9daf0e0f603362d31fbc231a344ab7
Author: Dennis Du Krøger <[email protected]>
Date: 2016-07-12T14:28:00Z
METAMODEL-1103: Anchor WildcardPattern to start
This makes sure the WildcardPattern anchors its test to the start of
the string, not only the end.
This comes with a minor performance penalty (quick test said 5-10% ),
but I think correctness trumps speed here.
I would have liked to compare speed with pre-compiled regexes
(`Pattern.quote()` the operand, replace `%` with `.*?` and anchor it
with `^` and `$`), but if the LIKE operand is inside a SelectItem,
that would mean compiling a new regex pattern for every row, which
would probably be _very_ expensive, so I opted not to try. There seem
to be some similar optimization of the IN operator, so I might be
wrong.
Fixes METAMODEL-1103
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