Re: DB2 Services - object_lock

Scott,

I wouldn't say I completely understand it yet to my satisfaction but you've
shown me what is possible and given me a nice working example and for that
I thank you very much.

I'll play around in visual explain and dig around in the literature a bit
more and see if I can't get a better handle on what's going on under the
covers.

thanks!
Craig

On Tue, 22 Oct 2019 at 16:55, Scott Mildenberger <smildenberger@xxxxxxxxxxxx>
wrote:

The Table function makes it look like a table to sql, it ends up being
equivalent to all the subselects in the other solution proposed but wraps
it in a single 'Table' so it is easier and cleaner to code. I don't know
if there is any performance difference, you could run Visual Explain on
both to see if it ends up being similar. What is inside the 'Table'
function does not have to be a function per se, usually for me it is a sql
statement. I know how to use it but I don't know if I can explain it well
- I have cases where it is just a sql statement that I want to use several
columns from at the top level query.

For example (from a Railroad) we have 'Waybills' what have many 'Movement
Events'. If I want to find a single Movement Event (based on some logic
like first one at a location) and tie it to the waybill the 'Table'
function allows this, using a Fetch First Row Only, in a single sql
statement. I even use it to find the last 'Movement Event' of a certain
type and tie it to a 'Waybill' even if that 'Movement Event' is from
another 'Waybill. Hope that is helpful but not sure.

I compare it to 'outer apply' in Sql Server, where I first used it. From
my understanding the 'Table' function allows the same functionality in Db2i.

Scott Mildenberger | Software Developer | Washington Corporations | 101
International Drive | Missoula, MT 59808 | Office: (406) 523-1536 |
www.washcorp.com

-----Original Message-----
From: RPG400-L <rpg400-l-bounces@xxxxxxxxxxxxxxxxxx> On Behalf Of Craig
Richards
Sent: Tuesday, October 22, 2019 9:06 AM
To: RPG programming on IBM i <rpg400-l@xxxxxxxxxxxxxxxxxx>
Subject: Re: DB2 Services - object_lock_info

Hi Scott,

Thank you very much - that works fine and does seem a lot cleaner.

I'm still struggling to understand exactly what is going on.
Whenever I write SQL, I always try to think of sets of data, what they
look like and how they join together.

A LEFT JOIN is straightforward.
But I've not used a Table Function before.

I can see that running something like:

select * from table(users()) u

calls the UDTF users() and returns a table.

I don't really have the mechanics of it clear in my mind as it pertains to
the SQL above - as you say, feeding the data though the CTE and also with
the join on 1=1 which if I understand it correctly would be some kind of a
cross join, which makes me wonder if it's kind of doing a cross join at
each row level.

If you have the patience and a bit more free time at some point I would be
grateful if you could help me understand the mechanics of exactly what is
going on here.

In any case, thanks so much for taking the time to look at my question and
provide a helpful and clear solution.
best regards,
Craig

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