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  2. RPG400-L
  3. December 2016

Re: Seeking a faster response to Where EXISTS or WHERE IN

On Thu, 2016-12-22 at 09:22 -0500, D Freinkel (a4g) wrote:
I am doing extracts from files based on records in file A



Select * from FILE_A where field_A in (Select FIELD_AA from FILE_B).
Or
Select * from FILE_A where field_A exists i (Select FIELD_AA from FILE_B
where FIELD_A = FIELD_B).
File_A and FILE_B both have about a million records.

Problem:

When running the program it takes a few minutes to build the sub-select.
Using CHAINS is instant, but I would prefer to use SQL.
Can anyone help with performance improvements?

With only a little knowledge of SQL, so working slightly blind, would it
not be possible to create a permanent view with the required join and
then just query the view?

Another possibility is that one, or both, of the files needs an index
built and its this on-the-fly index build that is slowing the SQL down
(I get the feeling there is more to the SQL than presented in the
example).

TIA
Darryl Freinkel


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