RE: SQL, Logical Files, Unions & Indexes.

From: Joe Pluta

For SQL tables and DDS described physical files there is an

architectural

difference. In DDS described files data validation happens as soon as a
record will be read (that's why garbage can be copied into physical

files

with *NOCHK). In SQL tables data validation happens as soon as a row

will

be
written, but there is no validation when a row will be read. Even with
Copy
*NOCHK no invalid data can be inserted into a SQL table. Because data
validation occurs at write time and not at read time, using SQL tables
will
gain performance.

Exactly.  Except in those rare circumstances where you do more writes than
reads (journals and logs), DDL should outperform DDS.

Note though that this performance boost is available to both native I/O and
SQL access.  That's why I use the term DDL rather than "SQL tables".  By
calling them "SQL tables" you encourage the misperception that the benefit
is only available to SQL, when in fact the exact same benefits are available
to native RPG access.

In short, DDL is a non-issue when choosing between SQL and native I/O.  It
makes both faster, in exactly the same way.

Joe