SQL Server Ranking Functions

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SQL Server Ranking Functions

WayneS

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April 19, 2010 at 8:48 pm

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Comments posted to this topic are about the item SQL Server Ranking Functions
Wayne
Microsoft Certified Master: SQL Server 2008
Author - SQL Server T-SQL Recipes
If you can't explain to another person how the code that you're copying from the internet works, then DON'T USE IT on a production system! After all, you will be the one supporting it!
Links:
For better assistance in answering your questions
Performance Problems
Common date/time routines
Understanding and Using APPLY Part 1 & Part 2
Forum Etiquette: How to post Reporting Services problems

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Forum Etiquette: How to post data/code on a forum to get the best help - by Jeff Moden
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How to Post Performance Problems - by Gail Shaw
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Jeff Moden SSC Guru Points: 1004561 More actions · Answer 1

Yowch... the formatting monster hit the code hard on this one. I hope Steve can fix it soon.

Glad to see you in the saddle again, Wayne. It's too late for me to read through it tonight but you can bet I'll read it in the morning over coffee.

--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.

Change is inevitable... Change for the better is not.

Helpful Links:
How to post code problems
How to Post Performance Problems
Create a Tally Function (fnTally)

SQLRNNR SSC Guru Points: 281334 More actions · Answer 2

Congrats on getting this article out Wayne.

Jason...AKA CirqueDeSQLeil
_______________________________________________
I have given a name to my pain...MCM SQL Server, MVP
SQL RNNR
Posting Performance Based Questions - Gail Shaw[/url]
Learn Extended Events

Michael Meierruth SSChampion Points: 10051 More actions · Answer 3

Wayne,

You state what I always wanted to hear stated, i.e. that ROW_NUMBER()'s ORDER BY is not the same as the SELECT's ORDER BY. Yet, always - haven't encountered an exception yet, when you perform a SELECT the output is always in the order specified by ROW_NUMBER()'s ORDER BY without the presence of an ORDER BY in the SELECT.

How do you explain that?

Oh yes, those ORDERBY and PARTITIONBY need fixing.:hehe:

mister.magoo SSC-Forever Points: 47174 More actions · Answer 4

Michael Meierruth (4/20/2010)
Wayne,
You state what I always wanted to hear stated, i.e. that ROW_NUMBER()'s ORDER BY is not the same as the SELECT's ORDER BY. Yet, always - haven't encountered an exception yet, when you perform a SELECT the output is always in the order specified by ROW_NUMBER()'s ORDER BY without the presence of an ORDER BY in the SELECT.
How do you explain that?
Oh yes, those ORDERBY and PARTITIONBY need fixing.:hehe:

You just have to look at the execution plan to see why they come out in that order without a specific order by on the select.

You will see a SORT to get the row numbers in the correct sequence. In the absence of any ORDER BY clause, there is no reason for the result set to be sorted again.

MM

select geometry::STGeomFromWKB(0x0106000000020000000103000000010000000B0000001000000000000840000000000000003DD8CCCCCCCCCC0840000000000000003DD8CCCCCCCCCC08408014AE47E17AFC3F040000000000104000CDCCCCCCCCEC3F9C999999999913408014AE47E17AFC3F9C99999999991340000000000000003D0000000000001440000000000000003D000000000000144000000000000000400400000000001040000000000000F03F100000000000084000000000000000401000000000000840000000000000003D0103000000010000000B000000000000000000143D000000000000003D009E99999999B93F000000000000003D009E99999999B93F8014AE47E17AFC3F400000000000F03F00CDCCCCCCCCEC3FA06666666666FE3F8014AE47E17AFC3FA06666666666FE3F000000000000003D1800000000000040000000000000003D18000000000000400000000000000040400000000000F03F000000000000F03F000000000000143D0000000000000040000000000000143D000000000000003D, 0);

SW_Lindsay SSCommitted Points: 1983 More actions · Answer 5

Nice and helpful article - Thanks. Just Curious...

To select eligible candidates in the first select you say

select * from @Candidates where MeetsEligibility = convert(bit,1);

Why do you convert the 1 into a bit? just saying 1 works. I know that the data type for MeetsEligibility is a bit and I'm just curious if there are efficiencies is converting explicitly like this or is it just a readability thing?

Steve

Ken Davis SSCarpal Tunnel Points: 4329 More actions · Answer 6

Excellent article. It's very readable with good examples.

WayneS SSC Guru Points: 95461 More actions · Answer 7

SW_Lindsay (4/20/2010)
Nice and helpful article - Thanks. Just Curious...
To select eligible candidates in the first select you say
select * from @Candidates where MeetsEligibility = convert(bit,1);
Why do you convert the 1 into a bit? just saying 1 works. I know that the data type for MeetsEligibility is a bit and I'm just curious if there are efficiencies is converting explicitly like this or is it just a readability thing?
Steve

Avoiding an "Implicit conversion". The literal 1 is an integer, resulting in the underlying field being converted to an integer to do the match... if there is an index on this field, it won't be used. Converting the 1 to a bit avoids the implicit conversion, and allows use of an index if one is present.

Personally, I wish there were system variables @@True and @@False of datatype bit, set to 1/0 respectively.

Wayne
Microsoft Certified Master: SQL Server 2008
Author - SQL Server T-SQL Recipes

If you can't explain to another person how the code that you're copying from the internet works, then DON'T USE IT on a production system! After all, you will be the one supporting it!

Links:
For better assistance in answering your questions
Performance Problems
Common date/time routines
Understanding and Using APPLY Part 1 & Part 2

SW_Lindsay SSCommitted Points: 1983 More actions · Answer 8

Thanks for the reply and I would agree those constants would be a great additions!

Andy Lennon SSCrazy Points: 2354 More actions · Answer 9

Michael Meierruth (4/20/2010)
Wayne,
You state what I always wanted to hear stated, i.e. that ROW_NUMBER()'s ORDER BY is not the same as the SELECT's ORDER BY. Yet, always - haven't encountered an exception yet, when you perform a SELECT the output is always in the order specified by ROW_NUMBER()'s ORDER BY without the presence of an ORDER BY in the SELECT.
How do you explain that?

i had the same question. is there a performance gain with the explicit conversion?

nvm, answered already :hehe:

busasquatch Grasshopper Points: 24 More actions · Answer 10

So, I've overcome the inability to display columnar formats in SSRS subreports by using ROW_NUMBER() along with some modulus "hack-a-math". Here's a brief use case.

Let's say that a customer can have one or more addresses. Using an SSRS subreport, you'd waste a lot of paper displaying these in one column. But, if you could give each address a "RowNumber" and "ColumnNumber", you could drop the addresses into a matrix using RowNumber and ColumnNumber as your groupings.

This revelation, single handedly, was my greatest self-discovery in SQL code in conjunction with SSRS, if I do say so myself.

-------------------

Brian Zive

Assistant Director, Systems

Business Intelligence Analyst

Massachusetts General Hospital

Development Office

___________________________________
Brian A. Zive
Assistant Director, Systems
Business Intelligence Analyst
Massachusetts General Hospital
Development Office

Thomas LeBlanc SSCrazy Eights Points: 8085 More actions · Answer 11

Great article, thanks for writing it and answering people's questions.

ThomasLL

Thomas LeBlanc, MVP Data Platform Consultant

magarity kerns SSCrazy Points: 2763 More actions · Answer 12

I see these functions in Oracle queries all the time and only partly understood what was going on - thanks for explaining it the SQL Server way! Now I can translate the Oracleisms!

Trey Staker SSCarpal Tunnel Points: 4796 More actions · Answer 13

Wayne, Great article! It came a long ways.

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WayneS SSC Guru Points: 95461 More actions · Answer 14

Jeff Moden (4/19/2010)
Yowch... the formatting monster hit the code hard on this one. I hope Steve can fix it soon.

I think it's all fixed now... all the code is in one block, and missing spaces have been added back in. Sure makes it a lot easier to read now. Thanks Steve!

Wayne
Microsoft Certified Master: SQL Server 2008
Author - SQL Server T-SQL Recipes

If you can't explain to another person how the code that you're copying from the internet works, then DON'T USE IT on a production system! After all, you will be the one supporting it!

Links:
For better assistance in answering your questions
Performance Problems
Common date/time routines
Understanding and Using APPLY Part 1 & Part 2

SQL Server Ranking Functions

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