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Re: minus vs. where not exists, vs. where not in

From: Mark Richard <mrichard_at_transurban.com.au>
Date: Sun, 21 Sep 2003 15:54:36 -0800
Message-ID: <F001.005D0A0A.20030921155436@fatcity.com>

I don't have any scientific proof but I imagine the sort_area_size could be different between "not exists" and "minus". When doing "minus" the entire select string would have to be compared for equality, which could be very large depending on your string.

Minus is probably an easier way (at least from a coding perspective) of comparing every column in a table, or incorporating complexity in the select statement.

Having said that. Each statement has it's pros and cons and I guess it depends on the volume of the various queries, etc. For example, if the have table A with 5 rows and table B with 1000000 rows executing "select a.field from a where not exists (select 1 from b where b.field = a.field) will result in 5 quick searches (assuming b.field is indexed) whereas "select a.field from a where a.field not in (select b.field from b)" will result in a full index read of b, as would "select a.field from a minus select b.field from b". Obviously different queries and different volumes will tip the scales in different directions.

Regards,

      Mark.

                                                                                                                                      
                      "Ryan"                                                                                                          
                      <rgaffuri_at_cox.net        To:       Multiple recipients of list ORACLE-L <ORACLE-L_at_fatcity.com>                  

> cc:
Sent by: Subject: minus vs. where not exists, vs. where not in ml-errors_at_fatcity .com 22/09/2003 03:59 Please respond to ORACLE-L

Do any of you have any cases when minus is superior in performance? Ive found 'not in' with a hash_aj to be the best option if the sub-query is significantly less 'costly' then the outer query. I dont mean cost in terms of the Explain Plan, I mean the work Oracle has to do to find a result set. It also depends on a proper hash_area_size

I find 'where not exists' to be best if the subquery is relatively close in cost to the outer query. Yes I know you cant make broad generalizations, but there has to be some 'narrow' generalizations you can make. Such as certain cases, etc...

what have you seen? There seems to be very little work in this area in the literature.

Does 'where not exist' need more or less sort_area_size space than minus?

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Author: Mark Richard
  INET: mrichard_at_transurban.com.au

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Received on Sun Sep 21 2003 - 18:54:36 CDT

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