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From "Laura Stewart" <scotsmat...@gmail.com>
Subject Tuning question - from 10.2 Doc Reviews
Date Mon, 02 Oct 2006 18:57:30 GMT
Hi -

In the 10.2 Doc Review of the Tuning Guide
http://wiki.apache.org/db-derby/TuningTenTwo
there is this comment:

In the file
http://db.apache.org/derby/docs/dev/tuning/rtuntransform472.html
there is a mention of rewriting queries:

 "Users can work around this possibility by writing the query like
this (which is not optimizable):(country... ) LIKE ?".

But this does not mention the rationale for doing so, which could be
benefical for the users in understanding the transformation.

One thought is that specifying "(country || '')" disables the
transformation because "(country || '')" evaluates to a Concatenate
node instead of a ColumnReference, which makes the expression "not
optimizable" and thus the transformation is skipped.

Does anyone have any additional information as to why "(country ||
'')" should be specified?

Thanks!

-- 
Laura Stewart

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