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From Army <a...@golux.com>
Subject Re: On DERBY-107 : ODBC Metadata functions
Date Thu, 27 Jan 2005 16:34:36 GMT
 > RPost wrote:
 > So then what is the difference between using a VTI and using a view?

Good question.  My use of VTIs has been limited to this particular discussion, but I think
the biggest difference is the 
language we use: with views, our playing field is the scope of SQL; with VTIs, we have pretty
much all of Java to work 
with, which gives us more freedom to do result set manipulations.

That said, though, it DOES look like everything we'd want to be able to do _can_ be done in
SQL (via subqueries), and 
hence option #2 in my previous email.  In effect, we'd be creating "view-like" functionality
through use of subqueries. 
  If we were to add an option #3 that is kind of like #2 but would actually be _creating_
views, then we'd have to 
answer the additional question of when do we create the views and where do we store them?
 Would be they become another 
set of SYS objects?  Such an approach would be more complicated than #2, I _think_...

The advantage of VTIs over subqueries and views is that we wouldn't have to change anything
at build time or database 
creation time--the general flow would remain exactly as it is now.  If we opt for subqueries
and/or Views, then we have 
to figure out how to create those subqueries/views automatically from the existing JDBC metadata
procedures (because 
again, we want to avoid having duplicate, humanly-maintained sets of queries), which requires
additional work at build 
or database creation time.

But then, like I said, since we _are_ able to do all the manipulations that ODBC requires
using SQL, maybe option #2 (or 
a view-based #3) would be preferable to doing it in Java...

If anyone with more experience with VTIs knows of other/more significant differences between
them and SQL views, feel 
free to say so...


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