Solved

Let's talk about query performance

Posted on 2014-12-09
3
133 Views
Last Modified: 2014-12-24
I have a question about query performance: retrieving values in the query with a pivot or left join versus retrieving them on the row of an ItemDataBound in the grid:

To get my grid values, I can do a "select * from UserProfile where ..."

I have a several fields in a table with responses that I would use a PIVOT or left join to create other columns:
like:
UserName   Age    City    State   Zip Haircolor
These are all in a responses table (these are examples, there are numerous responses); but none of these are in the UserProfile table. Each has its own row in the responses table.

As I said, I could use a pivot to create the query, or I could instead, when binding the grid, on the itembound go look up the data for that one row's user and display it in the grid at that time.

I'm thinking this will be better performance, because my grid will display maybe 100-500 results to a page, whereas, if I put this in a pivot, it will do it for every single record in the select clause, which could be maybe 5000 or 50,000 or whatever it gets to.

Also, in doing this, I might want to add to my main query some filtering, like:
select * from userprofile where exists (select 1 from ResponseTable where userprofile.userprofileid = ResponseTable .userprofileId and ResponseTypeId = 32)

So I *AM* going to be adding some subqueries to the actual query for filtering, but I don't need to really do this for some of the displayed fields such as, in my example, city, hair color (they won't be in the search filter). So entirely leaving out all the desired display results from the query and only using the exists clause on the search filters, plus adding the display data to the grid on load by doing queries at that time, seems to me would be the better performance.

I will probably look up about 6-10 values for each row that is displayed to the screen on the ItemDataBound; as opposed to putting PIVOT subqueries or even left joins on each of these 6-10 values:

For example, here's an actual query with only 2 of these values using a left join:
select username,
qaCity.textanswer as MyCity,
lvRace.ListValueName as MyRace
 from userprofile 
 left join qaset on qaset.userprofileid = userprofile.userprofileid
left join qafield qaCity 
  on qaset.qasetid = qaCity.qasetid
  and qaCity.questionvalueid = 34

  left join qaList qaRace 
  on qaset.qasetid = qaRace.qasetid
  and qaRace.questionvalueid = 32
    left join ListValue lvRace 
  on lvRace.ListValueId = qaRace.ListValueId
  where username <> ''

Open in new window


What do you think? What's the best performance method? 100 rows in the grid, or all 5000 rows in the query?

thanks.
0
Comment
Question by:Starr Duskk
[X]
Welcome to Experts Exchange

Add your voice to the tech community where 5M+ people just like you are talking about what matters.

  • Help others & share knowledge
  • Earn cash & points
  • Learn & ask questions
3 Comments
 
LVL 50

Accepted Solution

by:
Gustav Brock earned 167 total points
ID: 40491106
I believe the latter but nothing is shure. So much depends, and no one knows your details.

This is one of the type of questions where I recommend: Why not just check out both methods? It cannot take many hours, and then you have firm knowledge.

/gustav
0
 
LVL 34

Assisted Solution

by:ste5an
ste5an earned 167 total points
ID: 40491184
Please rephrase your question. What performance do you want to look at?

When it's about query performance, than it depends on your SQL Server instance. Especially cold buffers vs. hot buffers and proper indexing. Here it makes often no difference whether you generate the pivot here or return only the partial datasets. Often means: You need to test and measure it. There is no rule of thumb.

When it's about the overall performance, then calculating the pivot or an appropriate single resultset makes sense. Cause this reduces the round-trips from your application to the SQL Server. btw, your describtion does not sound like a pivot (changing rows to columns). It sounds like simply adding columns to the result set from different tables.

I don't understand your different cardinality estimates.

Can you give us a concise and complete example. Especially how does your data model looks like?
SELECT  username ,
        qaCity.textanswer AS MyCity ,
        lvRace.ListValueName AS MyRace
FROM    userprofile
        LEFT JOIN qaset ON qaset.userprofileid = userprofile.userprofileid
        LEFT JOIN qafield qaCity ON qaset.qasetid = qaCity.qasetid AND qaCity.questionvalueid = 34
        LEFT JOIN qaList qaRace ON qaset.qasetid = qaRace.qasetid AND qaRace.questionvalueid = 32
        LEFT JOIN ListValue lvRace ON lvRace.ListValueId = qaRace.ListValueId
WHERE   username <> ''

Open in new window

0
 
LVL 96

Assisted Solution

by:Bob Learned
Bob Learned earned 166 total points
ID: 40497311
Query optimization is part art and part science, and you can't even begin to optimize until we know what you are working with.
0

Featured Post

Is Your Team Achieving Their Full Potential?

74% of employees feel they are not achieving their full potential. With Linux Academy, not only will you strengthen your team's core competencies but also their knowledge of of the newest IT topics.

With new material every week, we'll make sure that you stay ahead of the game.

Question has a verified solution.

If you are experiencing a similar issue, please ask a related question

A long time ago (May 2011), I have written an article showing you how to create a DLL using Visual Studio 2005 to be hosted in SQL Server 2005. That was valid at that time and it is still valid if you are still using these versions. You can still re…
Calculating holidays and working days is a function that is often needed yet it is not one found within the Framework. This article presents one approach to building a working-day calculator for use in .NET.
NetCrunch network monitor is a highly extensive platform for network monitoring and alert generation. In this video you'll see a live demo of NetCrunch with most notable features explained in a walk-through manner. You'll also get to know the philos…
Monitoring a network: why having a policy is the best policy? Michael Kulchisky, MCSE, MCSA, MCP, VTSP, VSP, CCSP outlines the enormous benefits of having a policy-based approach when monitoring medium and large networks. Software utilized in this v…

707 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question