Re: AW: DDL Discussion continued

1 - You really don't see "actual data" in an index, view or LF. Now,
there may be enough information in an index that the query optimizer never
has to go to the actual table. For example if you CREATE INDEX and select
COL1 in the index and then do a SELECT COL1, COUNT(*) FROM TABLE1 GROUP BY
COL1 then the optimizer can use that index and never refer to the table
because the occurrences of COL1 are in there.

2 - The LF also doesn't seem to have the same page size, the index being
much bigger.
True. Give SQL's DDL a plus here.

3 - It seems in a LF, you can have SQL to create a view and therefore do
things that don't seem to be available with an index.
Let me rephrase this. In a LF you can combine attributes of a view and an
index. Yes it is true. And in V6R1 DDL was enhanced to do much of this.
However objects created with this are strictly there to replace using DDS
to create them. Target audience is those people still using HLL access
like CHAIN in RPGLE but want to create the objects with DDL and not DDS. I
do not believe the query optimizer will use objects created with the V6R1
options.

4 - It appears a LF can be accessed via a program to sort and present the
data to a program in a different way than how the data exists in a PF.
True. You can use SQL against a LF and alter the ordering sequence. But
you cannot perform SQL against an SQL index. They're there just for use
by the optimizer.
I mean the following in the best of light, really. If you're adamant
about only using SQL to access your files, why should you care? The
people who are gung ho to use the LF's are those who are using HLL's to
access the files and want those sort orders. The select/omits are just
gravy because a sql view would accommodate that (if you were accessing the
file view sql and could leave the index selection up to the optimizer).

5 - An index is accessed "under the covers" and from what I can see, can't
be accessed directly by a program.
A restating of bullet 4.

6 - On the system I work on, there a MANY LFs/access paths but they don't
show up as indexes via Navigator but an index does.
They do show up, they just show up as views.


Rob Berendt