RE: Slow query

>
>Dear all,
>
>Please find below the 2 queries :
>
>select dep_date from test_date1
>where to_char(dep_date,'dd-mon-yyyy') =
>'12-jan-2002'
>
>select dep_date from test_date1
>where TRUNC(dep_date) = to_DATE(
>'12-jan-2002','dd-mon-yyyy')
>
>The execution plan for both the queries shows a FTS
>on test_date1.
>
>Execution Plan
> 0 SELECT STATEMENT Optimizer=CHOOSE
> 1 0 SORT (AGGREGATE)
> 2 1 TABLE ACCESS (FULL) OF 'TEST_DATE1'
>
>The number of rows to be retrieved are 120010.
>
>The first query took 10msec to execute whereas the
>second took about 2
>secs.
>
>Could anyone help me figure out what the problem
>would be.
>
>TIA
>
>Best Regards
>Jai
>---------------------------------------------------
>-------

Which problem? I guess that, if the execution plans are identical, what you are experiencing is just the effect of caching. For a reason or another the data already was in memory in one case, and had to be loaded from disk in the other one. Check your trace statistics under SQL*Plus, logical IOs will probably be more or less identical and physical IOs wildly different.

Note that as long as you apply a function to dep_date, your only way to escape the FTS is (supposing 8.1.7 or above) function-based indexes. If dep_date is indexed, then you should use something like

       dep_date >= some_date and dep_date < some_date + 1 instead of

        trunc(dep_date) = some_date

It will allow for range scans.

Regards,

Stephane Faroult
Oriole

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Author: Stephane Faroult
  INET: sfaroult_at_oriolecorp.com

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