SQL Clone
SQLServerCentral is supported by Redgate
 
Log in  ::  Register  ::  Not logged in
 
 
 


how top clause works


how top clause works

Author
Message
sej2008
sej2008
Ten Centuries
Ten Centuries (1K reputation)Ten Centuries (1K reputation)Ten Centuries (1K reputation)Ten Centuries (1K reputation)Ten Centuries (1K reputation)Ten Centuries (1K reputation)Ten Centuries (1K reputation)Ten Centuries (1K reputation)

Group: General Forum Members
Points: 1023 Visits: 394
I found that TOP clause works little randomly with
Select TOP 50 percent * from Tablename as it is not giving exact 50 percent in my result set .how it gets the data reading from data pages.I have Idea that it is little random in working in respect to percent clause over datapages.
e4d4
e4d4
Ten Centuries
Ten Centuries (1.2K reputation)Ten Centuries (1.2K reputation)Ten Centuries (1.2K reputation)Ten Centuries (1.2K reputation)Ten Centuries (1.2K reputation)Ten Centuries (1.2K reputation)Ten Centuries (1.2K reputation)Ten Centuries (1.2K reputation)

Group: General Forum Members
Points: 1229 Visits: 2399
http://msdn.microsoft.com/en-us/library/ms189463.aspx


" PERCENT

Indicates that the query returns only the first expression percent of rows from the result set. Fractional values are rounded up to the next integer value.
"
ChrisM@Work
ChrisM@Work
SSC-Forever
SSC-Forever (43K reputation)SSC-Forever (43K reputation)SSC-Forever (43K reputation)SSC-Forever (43K reputation)SSC-Forever (43K reputation)SSC-Forever (43K reputation)SSC-Forever (43K reputation)SSC-Forever (43K reputation)

Group: General Forum Members
Points: 43125 Visits: 20015
sej2008 (1/15/2013)
I found that TOP clause works little randomly with
Select TOP 50 percent * from Tablename as it is not giving exact 50 percent in my result set .how it gets the data reading from data pages.I have Idea that it is little random in working in respect to percent clause over datapages.


What happens when you add ORDER BY to your query?

“Write the query the simplest way. If through testing it becomes clear that the performance is inadequate, consider alternative query forms.” - Gail Shaw

For fast, accurate and documented assistance in answering your questions, please read this article.
Understanding and using APPLY, (I) and (II) Paul White
Hidden RBAR: Triangular Joins / The "Numbers" or "Tally" Table: What it is and how it replaces a loop Jeff Moden
Exploring Recursive CTEs by Example Dwain Camps
Bhuvnesh
Bhuvnesh
SSChampion
SSChampion (13K reputation)SSChampion (13K reputation)SSChampion (13K reputation)SSChampion (13K reputation)SSChampion (13K reputation)SSChampion (13K reputation)SSChampion (13K reputation)SSChampion (13K reputation)

Group: General Forum Members
Points: 13884 Visits: 4077
sej2008 (1/15/2013)
I found that TOP clause works little randomly with
Select TOP 50 percent * from Tablename as it is not giving exact 50 percent in my result set .how it gets the data reading from data pages.I have Idea that it is little random in working in respect to percent clause over datapages.
sql server never gives guarantee about the order of data until/unless ORDER BY clause is mentioned. see http://msdn.microsoft.com/en-us/library/ms188385.aspx

-------Bhuvnesh----------
I work only to learn Sql Server...though my company pays me for getting their stuff done;-)
Grant Fritchey
Grant Fritchey
SSC Guru
SSC Guru (101K reputation)SSC Guru (101K reputation)SSC Guru (101K reputation)SSC Guru (101K reputation)SSC Guru (101K reputation)SSC Guru (101K reputation)SSC Guru (101K reputation)SSC Guru (101K reputation)

Group: General Forum Members
Points: 101469 Visits: 33014
Yes, it's going to be a little bit random in the number of rows it returns. However, for a given set of inputs against a constant set of data, you should see consistent results. But as soon as the data changes or the inputs change, all bets are off.

----------------------------------------------------
The credit belongs to the man who is actually in the arena, whose face is marred by dust and sweat and blood...
Theodore Roosevelt

The Scary DBA
Author of: SQL Server Query Performance Tuning and SQL Server Execution Plans
Product Evangelist for Red Gate Software
Bhuvnesh
Bhuvnesh
SSChampion
SSChampion (13K reputation)SSChampion (13K reputation)SSChampion (13K reputation)SSChampion (13K reputation)SSChampion (13K reputation)SSChampion (13K reputation)SSChampion (13K reputation)SSChampion (13K reputation)

Group: General Forum Members
Points: 13884 Visits: 4077
Grant Fritchey (1/15/2013)
as soon as the data changes or the inputs change, all bets are off.
yes i have also realized that for smaller set , we can see the consistent data more often but what make it unexpected or randomly ordered for larger set (for the time being, we can keep out parallelism,out of site here ) ?

-------Bhuvnesh----------
I work only to learn Sql Server...though my company pays me for getting their stuff done;-)
Grant Fritchey
Grant Fritchey
SSC Guru
SSC Guru (101K reputation)SSC Guru (101K reputation)SSC Guru (101K reputation)SSC Guru (101K reputation)SSC Guru (101K reputation)SSC Guru (101K reputation)SSC Guru (101K reputation)SSC Guru (101K reputation)

Group: General Forum Members
Points: 101469 Visits: 33014
Bhuvnesh (1/15/2013)
Grant Fritchey (1/15/2013)
as soon as the data changes or the inputs change, all bets are off.
yes i have also realized that for smaller set , we can see the consistent data more often but what make it unexpected or randomly ordered for larger set (for the time being, we can keep out parallelism,out of site here ) ?


Random ordering will absolutely not occur unless you are not using an ORDER BY statement. Then, it's all over Microsoft documentation and the web, there's no guarantee for data order without an ORDER BY statement. It's that simple. Any number of things can affect the order of the data returned, page splits and rearrange, different execution plans based on changing statistics or changing parameters, more. If you don't use an ORDER BY, you can't be surprised when the order is different from one time to the next.

----------------------------------------------------
The credit belongs to the man who is actually in the arena, whose face is marred by dust and sweat and blood...
Theodore Roosevelt

The Scary DBA
Author of: SQL Server Query Performance Tuning and SQL Server Execution Plans
Product Evangelist for Red Gate Software
Bhuvnesh
Bhuvnesh
SSChampion
SSChampion (13K reputation)SSChampion (13K reputation)SSChampion (13K reputation)SSChampion (13K reputation)SSChampion (13K reputation)SSChampion (13K reputation)SSChampion (13K reputation)SSChampion (13K reputation)

Group: General Forum Members
Points: 13884 Visits: 4077
thanks grant

-------Bhuvnesh----------
I work only to learn Sql Server...though my company pays me for getting their stuff done;-)
Go


Permissions

You can't post new topics.
You can't post topic replies.
You can't post new polls.
You can't post replies to polls.
You can't edit your own topics.
You can't delete your own topics.
You can't edit other topics.
You can't delete other topics.
You can't edit your own posts.
You can't edit other posts.
You can't delete your own posts.
You can't delete other posts.
You can't post events.
You can't edit your own events.
You can't edit other events.
You can't delete your own events.
You can't delete other events.
You can't send private messages.
You can't send emails.
You can read topics.
You can't vote in polls.
You can't upload attachments.
You can download attachments.
You can't post HTML code.
You can't edit HTML code.
You can't post IFCode.
You can't post JavaScript.
You can post emoticons.
You can't post or upload images.

Select a forum

































































































































































SQLServerCentral


Search