Re: Awesome news! LIMIT and OFFSET in TR3/TR11 -- bring on the SQL paging!

While it may be useful in a subfile, the real use is in client/server where
you don't have state.

It's a lot easier and quicker for the client side to simply request page 1,
page 2, page 3...instead of sending back 1,000 rows and letting the client
handle the paging.

Way back when (v5r?), you needed something like so to fetch rows 10 to 20

select *
from (select *
from (select iitnbr, idescr
from ioritemmst
order by idescr asc
fetch first 20 rows only
) as tmp1
order by idescr desc
fetch first 10 rows only
) as tmp2
order by idescr asc

and btw (originally?) the integers used in FETCH FIRST xxx ROWS couldn't be
variables. So you had to use dynamic SQL. So, not a speed demon, and the
performance gets worse the more pages you go down. But better than trying
to send the whole results set.

Now when ROW_NUMER() came about, it made things easier...

select iitnbr, idescr
from (select iitnbr, idescr
, row_number() over (order by idescr) as rn
from ioritemmst
) as tmp
where rn between 11 and 20
order by idescr

Now with LIMIT and OFFSET, all you'd need is
select iitnbr, idescr
from ioritemmst
order by idescr
limit 10 offset 10

I'd imagine the IBM is doing some magic under the covers with open data
paths so that when the next page is requested, it's quicker than the older
methods.

Lastly, other DBs have LIMIT and OFFSET, so if you're porting it's good
that IBM i has them now too.

Charles



On Mon, Oct 12, 2015 at 11:41 AM, <darren@xxxxxxxxx> wrote:

Excited to see this...

http://www.mcpressonline.com/db2/what-s-new-in-db2-for-i-with-tr3.html

No more jumping through hoops to return a page at a time.

How would you use something like this? I assume we're talking about
filling a page of a subfile, and for that I'm currently using a cursor.
Perhaps with my limited imagination, I can only think to use this to
perhaps not use a cursor, and track the last row read to feed into that
statement, but wouldn't that be pretty inneficient to tell it to skip the
first 100 rows or whatever you're now paged down to?

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