Re: SQL select via logicals

[DAsmussen <DAsmussen@xxxxxxx>]

John,

In a message dated 97-12-06 18:02:31 EST, you write:

> <SNIP> (Actually, I wrote)
>  No, your records will not necessarily be returned based upon the S/O
criteria.
>  SQL evaluates the n (used to be five, may now be ten or more) oldest
logical
>  files by creation date based upon the ORDER BY and WHERE clauses to decide
>  whether or not it needs to build an access path.  If you have an ORDER BY
>  statement that doesn't match the WHERE (select/omit) and key of those older
>  logicals, you may not get the logical specified in your SELECT statement.
>  <SNIP>
>  Dean Asmussen
>  
>  Hey Dean
>  
>  I thought it looked at the oldest first too.  But Kent Milligan of
Rochester
>  DB2/400 said the following;
>  
>  <Kent Milligan said;>
>  "A couple of ways to influence the optimizer is by specifying the logical 
>  file directly on the SQL statement so that the optimizer does look at that
>  access path first.  The other trick is recreating the index - due to the 
>  way index information is organized in the underlying database file object
>  the optimizer is typically given indexes in a most recently created order
>  (eg, first index examined, tends to be the index most recently created). 
>  These methods provide ways of influencing the optimizer, but aren't 
>  guaranteed to work in all cases."

Darn, I knew _that_ -- I just keep forgetting these aritrary rules!  At least
my statement that the specified logical may not be used was correct...

>  So I guess it's the Newest to Oldest.

Yep, that's why we use the physical.  Even if you verify via STRDBG that the
correct logical was chosen by your program, a later compile of a logical can
upset the entire apple cart.

Regards!

Dean Asmussen
Enterprise Systems Consulting, Inc.
Fuquay-Varina, NC  USA
E-Mail:  DAsmussen@aol.com

"Mondays are the potholes in the road of life." -- Tom Wilson
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