RE: Need advice on how to index UNIONed tables

If or which index is used is determined at runtime.
It there are no where conditions, i.e. if the complete table is read, there is no need to use an index, i.e. it makes no sense to use an index in this situation.
That is why no index is used and why you are not getting an index advice.

You may read the indexing and statistics strategy white paper from Mike Cain and Kent Miligan to understand how indexes are used and to find your own indexing strategy
(https://www-356.ibm.com/partnerworld/wps/servlet/download/DownloadServlet?id=G_mhBFTHFjyiPCA$cnt&attachmentName=ibm_db2_for_i_indexing_methods_and_strategies.pdf&token=MTUzMDI0NzYwNjgyMQ==&locale=en_ALL_ZZ)

Mit freundlichen Grüßen / Best regards

Birgitta Hauser

"Shoot for the moon, even if you miss, you'll land among the stars." (Les Brown)
"If you think education is expensive, try ignorance." (Derek Bok)
"What is worse than training your staff and losing them? Not training them and keeping them!"
„Train people well enough so they can leave, treat them well enough so they don't want to.“ (Richard Branson)


-----Original Message-----
From: MIDRANGE-L <midrange-l-bounces@xxxxxxxxxxxx> On Behalf Of a4g atl
Sent: Donnerstag, 28. Juni 2018 20:43
To: midrange-l@xxxxxxxxxxxx
Subject: Re: Need advice on how to index UNIONed tables

I ran it through VE and it did not suggest anything.

There are indexes over the individual tables.

Darryl


On Thu, Jun 28, 2018 at 1:14 PM Justin Taylor <JUSTIN@xxxxxxxxxxxxx> wrote:

True, but VE should still be able to make recommendations.


________________________________________
From: Charles Wilt [charles.wilt@xxxxxxxxx]
Sent: Thursday, June 28, 2018 12:02 PM
To: Midrange Systems Technical Discussion
Subject: Re: Need advice on how to index UNIONed tables

Indexes are built over the individual tables...

Charles

On Thu, Jun 28, 2018 at 10:57 AM a4g atl <a4ginatl2@xxxxxxxxx> wrote:

I tried using the index adviser, but it did not provide any help.
Run and explain gave no recommendations.

Darryl.


On Thu, Jun 28, 2018 at 11:47 AM a4g atl <a4ginatl2@xxxxxxxxx> wrote:

Thanks

Trying UNION ALL

Where do I add the indexes.? I tried in the SELECT statements but
they gave an error.

Thanks

Darryl.


On Thu, Jun 28, 2018 at 10:49 AM Birgitta Hauser <

Hauser@xxxxxxxxxxxxxxx

wrote:

Do you need the rows to be checked for duplicates and remove

duplicates?

If not replace UNION with UNION ALL.

Additionally you need indexes for both tables, depending on

(additional)

WHERE Conditions.

Mit freundlichen Grüßen / Best regards

Birgitta Hauser

"Shoot for the moon, even if you miss, you'll land among the stars."

(Les

Brown)
"If you think education is expensive, try ignorance." (Derek Bok)
"What is worse than training your staff and losing them? Not
training

them

and keeping them!"
„Train people well enough so they can leave, treat them well
enough so they don't want to.“ (Richard Branson)


-----Original Message-----
From: MIDRANGE-L <midrange-l-bounces@xxxxxxxxxxxx> On Behalf Of
a4g

atl

Sent: Donnerstag, 28. Juni 2018 17:12
To: midrange-l@xxxxxxxxxxxx
Subject: Need advice on how to index UNIONed tables

I have a need to create UNIONed tables into a VIEW to give me
access

to

data
in both libraries from a single SELECT.

The UNION is working but the response is very slow.

I created the unions very simply example:

Select * from lib1/file_a
UNION
Select * from Lib2/File_a

I will experiment adding the order by in the SELECT.

What is the best practice?

TIA

Darryl Freinkel
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