Query refinement

Cathy,

It doesn’t really matter which tool you use. The performance of the query
will be dependent on the quality of the query to a large degree. If you want to
increase performance, you need to get comfortable with Execution Plans.

Here’s a whitepaper I wrote on the subject and it shows how you can use
Toad for help.

http://www.toadworld.com/Portals/0/ToadTechPapers/Explain%20This%20-%20Toad%20Whi
te%20Paper.pdf

Jeff

you need to get comfortable with Execution Plans

Not just that, Cathy has a lot of learning to do.

Hey Cathy, code performance is a rather lengthy topic. A lot of the stuff you
will pick up will be experience over time. I don’t mean this statement to
be frustrating to you but to be a realization that what you just asked for help
on is a very complex subject. I think the only solid rule anyone can say about
performance without knowing your specific situation is:

“Everything is situational.”

Even reading an execution plan to decipher where you went wrong is going to be
situational.

For example, if your query returns a rather large set of the available data, 90%
for sure, you should almost definitely avoid the use of indexes and do at least
one full table scan. On the other hand, if your query returns a rather small
subset of the data, say 2%, then you should almost definitely use an index and
avoid full table scans.

Note the use of the “almost” portion of that :wink:

That example should tell you something beyond the rule that everything is
situational: understanding your data is very important to authoring high
performance queries. The more complicated the query, the more
“situational” type recommendations you are likely to receive.

Is there perhaps a fellow software developer you work with who is an old hand
with regards SQL optimization who would be willing to be a “performance
mentor”?

RAS

Morning all,

Not just that, Cathy has a lot of learning to do.
True, but if I may be so bold, when she does know how to code SQL, I
would advise getting a copy of Guy Harrison's book "Oracle SQL High
Performance Tuning".

It's not for absolute beginners, but once you can write SQL, read it and
learn from it.

Cheers,
Norm. [TeamT]

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