SQL select by date

[Rich Duzenbury <rduz-midrange@xxxxxxxxxxxxxxxxxxx>]

Hi,

I want to select some records via SQL that contain a transaction posting
date via a date range.  Unfortunately, the dates are stored in
components: 

POSTCY  4,0
POSTMM  2,0
POSTDD  2,0

In order to do a range selection in a where clause, the date fields must
be concatenated together in some way.

This file has millions of records, and there is an index by POSTYY,
POSTMM, POSTDD.

What is the correct (efficient) way that will hopefully use the existing
index?  

Thanks.
--
Regards,
Rich

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