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Index with two date fields using comparison operators
Posted by: Istvan Zakar
Date: December 05, 2010 05:38PM

Hi,

I have a table for storing historical data with two date fields (valid_from, valid_till). I have indexed this two fields with a B-Tree index. If I run a query like this:

select * from subreg where
valid_from = '2011-01-22' and
valid_till = '2011-01-25';

it works fine. If check the explain I can see, that the key length is 6.

If I change the query slightly:

select * from subreg where
valid_from = '2011-01-22' and
valid_till > '2011-01-23';

it's still okay.

But this query takes long time to execute:

select * from subreg where
valid_from < '2011-01-23' and
valid_till > '2011-01-23';

I suppose the index is used only for the first column in this case (at least the length of the key is only 3 in this case). Is there anything I can do to increase the performance of this query?

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