Re: RRN and Database Files -- RPG400-L

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On Fri, Jan 9, 2009 at 12:32 PM, Birgitta Hauser <Hauser@xxxxxxxxxxxxxxx> wrote:

For reasons unknown, the query engine on the i will do a full table scan

when you have RRN in the where clause of a statement.
A full table scan will be used, because indexes (or access paths) can only
be created over existing columns within the based table.
RRN is no "real" column and therefore no index can be used.
Even in release 6.1. where derived indexes, where new columns can be defined
can be created it is not possible to create an index over the RRN.

But obviously some sort of access path exists over RRN, as RPG can
chain (quickly) via RRN.

Oracle has the ROWID pseudo-column, which allows fast access to a
particular row. The IBM i has the ROWID() function, but it doesn't
work the same. It would appear that DB2 for z/OS support a ROWID()
like Oracle's.

MS SQL Server doesn't support RRN or ROWID.

Not saying that use use is a good idea. But if RRN() is going to be
there, I see no reason why it shouldn't return a single row quickly.

Charles

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