The answer is a solid "maybe"... Although from an end-user perspective a
CTE and a view can help to solve the same problem (i.e. separating a
complex query into manageable pieces), they have slightly different
semantics from an SQL language perspective. As a result, the optimizer may
end up implementing them somewhat differently. Without knowing more
details about the query and seeing the VE, it's impossible to say for sure
whether a view would improve performance, but it is worth a try.
DB2 for IBM i / SQL Optimizer
"MIDRANGE-L" <midrange-l-bounces@xxxxxxxxxxxxxxxxxx> wrote on 12/01/2021
From: "Greg Wilburn" <gwilburn@xxxxxxxxxxxxxxxxxxxxxxx><midrange-l@xxxxxxxxxxxxxxxxxx>,
To: "Midrange Systems Technical Discussion"
Date: 12/01/2021 03:25 PM
Subject: [EXTERNAL] SQL View vs CTE
Sent by: "MIDRANGE-L" <midrange-l-bounces@xxxxxxxxxxxxxxxxxx>
I have a complex SQL statement that I'm going to use as a data
source for a browser application. In ACS Run SQL scripts it
consistently takes about 22 seconds to run. The statement contains
a CTE followed by a join to the CTE. The files involved have a
large number of records.
So I'm wondering if someone can tell me whether creating an SQL View
in place of the CTE would yield any performance increase (I haven't
spent much time looking at the Visual Explain in ACS).
I'm thinking it wouldn't make much difference.
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Greg WilburnDirector of IT
301.895.3792 ext. 1231
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Grantsville, MD 21536
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