Re: Best approach for Embedded SQL SELECT in V7R1

[Charles Wilt <charles.wilt@xxxxxxxxx>]

As far as I recall, nothing has been added to 7.1 that helps here...so the
following applies from at least v5r4 forward.

Yes, if you want to see any performance improvement in SQL vs. RLA, you'll
need to fetch multiple records.  Either into a MODS or an array.  I prefer
array's and IIRC v5 somthing is where IBM added support for fetching into
them.

Here's the key: SQL doesn't support the idea of "position to" like RLA
does.  For example, with RLA, I can position to a key value (say '123',
then page backward or forward.  To do this via SQL requires either two
cursors  (WHERE >= '123', WHERE < '123') or closing reopening the cursor.

With SQL you're better off with using "subset by".  The resulting serahc
functionality can be considerably more flexible and powerful (think RegEx
for example); but your users may need some time and training to accept it.

HTH,
CHarles


On Tue, Nov 6, 2012 at 9:37 AM, Michael Ryan <michaelrtr@xxxxxxxxx> wrote:

> Hi folks...looking for opinions/ideas here. I'm working with a program that
> declares a cursor, then does a FETCH NEXT to iterate through the result set
> and fill a subfile. It looks like this:
>
>              DECLARE C1 CURSOR FOR
>              Select * From Inventory
>              Where...<where and order by clauses>
> ...
>          Exec SQL
>             Fetch Next
>               From C1
>               Into :WkInventory;
>
> Where WkInventory is an externally described DS based on the Inventory
> file. The data is then moved from WkInventory to the subfile, and the
> subfile is eventually displayed.
>
> I *think* that performance would improve by FETCHing multiple rows into a
> MODS or an array in a data structure, rather than esentially performing RLA
> with SQL. Recently upgraded to V7R1, so I'm looking for the best approach
> at this OS level - I know I can do more than I could do in V5R4. My first
> thought is a MODS and specifying a number on the FETCH. But then I need to
> be concerned about 're-FETCHing' when I run out of rows for my subfile,
> right? Would an array make more sense than a MODS?
>
> I want to use SQL where it makes sense and RLA where it makes sense. I need
> to work through this concept so I can use this technique as I go forward.
> Ideas, opinions, code samples all welcome. Thanks in advance!
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