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Clarity vs Speed Expand / Collapse
Which of these pieces of code would you use
Poll ResultsVotes
a) Series of "If" statements
 
33.33%
2
b) The function call
 
16.67%
1
c) The select statement
 
50%
3
Member Votes: 6, Anonymous Votes: 0. You don't have permission to vote within this poll.
Author
Message
Posted Friday, October 26, 2007 11:58 AM
Grasshopper

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The following all produce the same results. Which would you use in your production code and why
a) a series of If statements
if @gross_pay < 35.17
select @boo = 0
else if @gross_pay >= 35.17 and @gross_pay < 151
select @boo = 40
else if @gross_pay >= 151 and @gross_pay < 201
select @boo = 50
else if @gross_pay >= 201 and @gross_pay < 251
select @boo = 60
else if @gross_pay >= 251 and @gross_pay < 301
select @boo = 70
else if @gross_pay >= 301 and @gross_pay < 351
select @boo = 80
else if @gross_pay >= 351
select @boo = 90

b) a function that calls the same series of if statements in "a)"
SET @boo = dboMaxTempDeduction(@gross_pay)

c) a Select statement
SET @Boo = (SELECT 40 WHERE Exists(SELECT 1 WHERE @Inc > 32.5)) + isnull((SELECT ((convert(int, (@inc/50)) -3) * 10) + 10 WHERE EXISTS( SELECT 1 WHERE @inc > 150.01)),0) - isnull((SELECT ((convert(int, ((400.01 - @inc)/50)) -1) * -10) WHERE EXISTS( SELECT 1 WHERE @inc > 400)),0)

The speed of execution for each of these in microseconds is is a) 4.86 b) 51.64 c) 8.26
Post #415562
Posted Friday, October 26, 2007 12:51 PM


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To be honest I wouldn't use any, instead I'd use a range table such as below, avoids hardwiring values


create table Ranges(GrossPayMin decimal(10,3) not null,
GrossPayMax decimal(10,3) not null,
Boo int not null,
primary key(GrossPayMin,GrossPayMax))
insert into Ranges(GrossPayMin,GrossPayMax,Boo) values(0, 35.17,0)
insert into Ranges(GrossPayMin,GrossPayMax,Boo) values(35.17,151,40)
insert into Ranges(GrossPayMin,GrossPayMax,Boo) values(151,201,50)
...
insert into Ranges(GrossPayMin,GrossPayMax,Boo) values(351,99999,90)

select @Boo=Boo
from Ranges
where @gross_pay>=GrossPayMin
and @gross_pay<GrossPayMax





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Post #415590
Posted Friday, October 26, 2007 1:54 PM
Grasshopper

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Agreed. This is another perfectly viable method. Putting it through the same Iteration test it comes out as the third slowest (23 microseconds per iteration). If having the data matrix dynamic is a requirement to the problem then it is the ONLY reasonable solution.
Post #415611
Posted Friday, October 26, 2007 2:15 PM
Right there with Babe

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Is it faster if a temp variable is used instead of a temp table?
How about if the table was pre-created? The dynamic solutions are still hardcoding values, to be truly dynamic they would be in an existing lookup table and there wouldn't be any insert overhead.

Post #415617
Posted Friday, October 26, 2007 2:44 PM
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Actually I might do this personnally


SET @boo = (CASE
WHEN @gross_pay < 35.17 THEN 0
WHEN @gross_pay < 151 THEN 40
WHEN @gross_pay < 201 THEN 50
WHEN @gross_pay < 251 THEN 60
WHEN @gross_pay < 301 THEN 70
WHEN @gross_pay < 351 THEN 80
ELSE 90
END)



Post #415626
Posted Friday, October 26, 2007 2:50 PM
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Sorry, it has both clarity and should have the speed you want.


Post #415627
Posted Friday, October 26, 2007 3:29 PM
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I have tried the more dynamic lookup suggested earlier with both a fixed table and the table variable. Interestingly enough there is not a significant difference in the timing.

For raw speed the verbose If statements wins over everything. The more convoluted select statement is next, followed by the Select then the function call.

A side note: I was challenged to come up with my own version of the type of "Max" function that SQL lacks - the max between two variables - and this employs that methodology. There are few places one needs it but if you do this is as fast as it is ugly.
Post #415636
Posted Friday, October 26, 2007 3:31 PM
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That is an excellent solution!
Post #415637
Posted Friday, October 26, 2007 5:32 PM


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Heh... no matter how you swing it, this whole thing is RBAR... if it's for a GUI single row proc... no problem... if it even comes near a batch, big problem.

--Jeff Moden
"RBAR is pronounced "ree-bar" and is a "Modenism" for "Row-By-Agonizing-Row".

First step towards the paradigm shift of writing Set Based code:
Stop thinking about what you want to do to a row... think, instead, of what you want to do to a column."

(play on words) "Just because you CAN do something in T-SQL, doesn't mean you SHOULDN'T." --22 Aug 2013

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Post #415656
Posted Saturday, October 27, 2007 2:47 PM
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What you are saying is true. In the real world where this code was snatched from with a little bit of salty refactoring I avoided this process entirely. Goes back to an old axiom "If you don't like the answer - rethink the question." That is off subject though.

I was very interested in where experienced, practical professionals would come down on the question of having to choose between "verbose maintainable and slow" vs "nicely black box but very slow" vs "efficient but not so obvious". I wanted to use some sample code that would demonstrate these notions. I fear I went afoul there. My apologies if I wasted anyones time.

There are soapboxes everywhere but given a sort of "Sophies Choice" of code I wondered which side serious professionals would come down on. As a person who manages, trains or mentors people on a regular basis I keep trying to understand development choices others make as a part of training my thinking. For various reasons that responsibility brought me to where I had a need to visit the "clarity vs Speed" issue.

Thank you to all of you who responded. Each and every response was very instructional.
Post #415743
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