MS SQL order by with "over" statement and row_number()

Brad Bansner
Brad Bansner used Ask the Experts™
on
I have a query I use frequently that someone helped me write several years ago, which I often create variations on. I thought I understood exactly what it does, but I am finding a discrepancy with the "order by" that I don't understand.

This query does what I want, which is simply an alphabetical sort on the "description" column:

select distinct
	description
from
	(select row_number() over (order by description) as rownum, description
		from tbl_product
		where (itemid='LUGS & H-TAPS : YAV2CLTC10FX' or itemid='LUGS & H-TAPS : YAV2CL2TC14E2FX')) as qryresults

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RESULT:

description
"LUG COMPRESSION # 2 AWG FLEX 1 HOLE #10 STUD STANDARD BARREL 0.68"" TONGUE WIDTH BROWN W/ INSP WNDW BURNDY"
"LUG COMPRESSION # 2 AWG FLEX 2 HOLE 1/4"" STUD 3/4"" CENTER STANDARD BARREL 0.68"" TONGUE WIDTH BROWN W/ INSP WNDW BURNDY"

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This query returns the same two results, but the "order by" is backwards:

select distinct
	itemid, description
from
	(select row_number() over (order by description) as rownum, itemid, description
		from tbl_product
		where (itemid='LUGS & H-TAPS : YAV2CLTC10FX' or itemid='LUGS & H-TAPS : YAV2CL2TC14E2FX')) as qryresults

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RESULT:

itemid 	description
LUGS & H-TAPS : YAV2CL2TC14E2FX	"LUG COMPRESSION # 2 AWG FLEX 2 HOLE 1/4"" STUD 3/4"" CENTER STANDARD BARREL 0.68"" TONGUE WIDTH BROWN W/ INSP WNDW BURNDY"
LUGS & H-TAPS : YAV2CLTC10FX	"LUG COMPRESSION # 2 AWG FLEX 1 HOLE #10 STUD STANDARD BARREL 0.68"" TONGUE WIDTH BROWN W/ INSP WNDW BURNDY"

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The only difference between the two is the "itemid" column present in the "select" clause (twice). I'm not understanding why selecting that column should cause the sorting to be backwards.

Thank you!
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Pawan KumarDatabase Expert
Awarded 2016
Top Expert 2016

Commented:
In one query you are sorting on itemid, description and in another you are doing only on description.

Thats why.
, DISTINCT will give you distinct records, order will be decided on the columns selected.

Innner row_number() -- does not matter.
Brad BansnerWeb Developer

Author

Commented:
I thought "order by description" would determine the order. I don't have "order by itemid,  description". How can I modify the second query so that it will return both itemid and description, but be sorted on description?
Scott PletcherSenior DBA
Most Valuable Expert 2018
Top Expert 2014

Commented:
The ORDER BY in a ROW_NUMBER clause is used to assign values, it does not necessarily control the order in which rows are returned from the query.

An inner query order is never a guarantee of the order of rows for an outer query.

In short, if you want a specific order of rows returned by a query, you must ORDER BY in the outer query, such as:

select distinct
      itemid, description
from
      (select row_number() over (order by description) as rownum, itemid, description
            from tbl_product
            where (itemid='LUGS & H-TAPS : YAV2CLTC10FX' or itemid='LUGS & H-TAPS : YAV2CL2TC14E2FX')) as qryresults
order by description, itemid

Or even:

select distinct
      description
from
      (select row_number() over (order by description) as rownum, description
            from tbl_product
            where (itemid='LUGS & H-TAPS : YAV2CLTC10FX' or itemid='LUGS & H-TAPS : YAV2CL2TC14E2FX')) as qryresults
order by description

The distinct caused SQL to do a sort, which is why the rows were in order, but that was incidental/accidental, since an order by clause was not used.
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Database Expert
Awarded 2016
Top Expert 2016
Commented:
Here it is , You are not using row_num , why you have added it.

Sample example

select distinct
      itemid, description
from
      (select row_number() over (order by description) as rownum, itemid, description
            from tbl_product
            where (itemid='LUGS & H-TAPS : YAV2CLTC10FX' or itemid='LUGS & H-TAPS : YAV2CL2TC14E2FX')) as qryresults
ORDER BY description

select distinct
      description
from
      (select row_number() over (order by description) as rownum, description
            from tbl_product
            where (itemid='LUGS & H-TAPS : YAV2CLTC10FX' or itemid='LUGS & H-TAPS : YAV2CL2TC14E2FX')) as qryresults
ORDER BY description
Brad BansnerWeb Developer

Author

Commented:
I guess I didn't understand that before. It always seemed to work in the past, maybe I just got lucky. Anyway, thanks for your help!
Brad BansnerWeb Developer

Author

Commented:
I am using row_num in my final query, I was just trying to give you a stripped down version of my more complicated working query.
Pawan KumarDatabase Expert
Awarded 2016
Top Expert 2016

Commented:
Great that you got it !! Excellent.
Brad BansnerWeb Developer

Author

Commented:
Sorry, I thought I had already assigned points.
Scott PletcherSenior DBA
Most Valuable Expert 2018
Top Expert 2014

Commented:
Interesting points assignment.  Good luck with future qs.
Brad BansnerWeb Developer

Author

Commented:
Oh geez, I apologize! I did not realize there was more than one respondent. Somehow missed that.
Scott PletcherSenior DBA
Most Valuable Expert 2018
Top Expert 2014

Commented:
Oh, ok, that makes sense.  Now maybe it's just me, but I thought my comments were more useful and on point (of course, maybe that's just me favoring my own answer :-) ).

[To be clear, I am not suggesting he just copied my answer, as the times are extremely close, and cross-posting is unavoidable on a site like this.]

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