Re: Evaluation of SQL SELECT WHERE's

I'd solve the problem as follows:

with myfile( dept, name, years_experience, years_college, PMP)
as (values( 'X', 'Tom ', 8, 3, 'NO '),
( 'X', 'Dick ', 2, 5, 'YES'),
( 'X', 'Harry', 2, 4, 'YES'),
( 'X', 'Peter', 12, 3, 'YES'),
( 'X', 'Tim' , 5, 2, 'YES'))
Select Dept, Name, Years_Experience, Years_College, PMP,
Case When Years_experience > 10 then 1 Else 0 End as "Experience",
Case When Years_College >= 4 then 1 Else 0 End as "College",
Case When PMP = 'YES' Then 1 Else 0 End as "With PMP"
from MyFile
Where Years_Experience > 10
or Years_College >= 4
or PMP = 'YES'
Order By "Experience" Desc, "College" Desc, "With PMP" Desc, Dept, Name ;

BTW the query optimizer does not need to read the table several times.
It can even use multiple (different) indexes for the same table in the same
query, return a bit map with in indicator set to on for all matching rows
for each index, and then merge the bitmaps before accessing the data/rows
themselves.
There are also a lot of other techniques/temporary objects, hash tables,
hash scans etc for accessing the data as fast as possible.
Just run your query through visual explain and have a look what happens.


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@xxxxxxxxxxxxxxxxxx> On Behalf Of
Arnie
Flangehead
Sent: Montag, 12. Oktober 2020 14:30
To: Midrange Systems Technical Discussion <midrange-l@xxxxxxxxxxxxxxxxxx>
Subject: Re: Evaluation of SQL SELECT WHERE's

p.s. I forgot to put the second level into the yc ranking, without which
you
might get an occasional false result. Should read:

rank() over ( partition by dept order by
years_college desc,
years_experience desc ) as yc,
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