index fast full scan vs index range scan

From: Senthil Ramanujam <sramanujam_at_comcast.net>
Date: Sun, 21 Mar 2004 19:25:57 -0500
Message-ID: <405E3295.5010508@comcast.net>

List,

I may need a little help here understanding Oracle optimization. How will the following code be treated in Oracle optimizer?

table has a column called "code". code is (not null) varchar2(24). it has a regular index on this column. :b1 would have any valid value.

exec :b1 := 'xxx'; ... select ... from ... where code like :b1 || '%'*

the above code lets the optimizer to choose "index fast full scan". but changing the code slightly as given below:

exec :b1 := 'xxx' || '%'; ... select ... from ... where code like :b1*

lets the optimizer to choose "index range scan". obviously, the second method runs much faster.

Any thoughts or inputs are much appreciated.

thanks.

senthil

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Received on Sun Mar 21 2004 - 18:22:59 CST