try..catch and union all

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try..catch and union all

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rightontarget

Posted Monday, October 29, 2012 12:48 PM

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Hi all,
I have the following construct:

select name, value 
from 
  ( select name, value from view1
    union all
    select name, value from view2
    union all
    select name, value from view3
   )

If any of the selects in the from fails, I need to display: 'no_data',0
When I try to wrap each select in try/catch, SS screams at me.
What are my options?

Thanks,

Post #1378416

Sean Lange

Posted Monday, October 29, 2012 12:55 PM

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eugene.pipko (10/29/2012)

Hi all,
I have the following construct:

select name, value 
from 
  ( select name, value from view1
    union all
    select name, value from view2
    union all
    select name, value from view3
   )

If any of the selects in the from fails, I need to display: 'no_data',0
When I try to wrap each select in try/catch, SS screams at me.
What are my options?

Thanks,

You can't just toss try/catch block in the middle of a query. What do you mean by "If any of the selects in the from fails"? Are you expecting an error when selecting from a view? Or do you mean "fail" because there are no rows returned?

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Post #1378421

rightontarget

Posted Monday, October 29, 2012 1:05 PM

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Thanks for reply. By fails, I mean, the statement returns an error. Usually timeout error.

Post #1378427

Sean Lange

Posted Monday, October 29, 2012 1:13 PM

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eugene.pipko (10/29/2012)

Thanks for reply. By fails, I mean, the statement returns an error. Usually timeout error.

You need to handle that in the front end. Your statement needs to complete before a try/catch will help you with that. A timeout is not a sql error, it is a connection error.

_______________________________________________________________

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Cross Tabs and Pivots, Part 1 – Converting Rows to Columns
Cross Tabs and Pivots, Part 2 - Dynamic Cross Tabs

Post #1378432

rightontarget

Posted Monday, October 29, 2012 2:12 PM

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What about any other error? There is no front end. The result is emailed to the user.
I guess what I am trying to do is to let the other 2 parts of the union all work and report 'no_data',0 for the part that failed.
Is it possible is SS 2K8R2?

Post #1378459

Sean Lange

Posted Monday, October 29, 2012 2:42 PM

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eugene.pipko (10/29/2012)

The front end doesn't have to be visual. Something gets the results and emails it. Given what you are describing I wouldn't bother trying to capture other types of errors. Let what process runs your query handle it. Put your try/catch there and you should be good to go. It sounds like it doesn't matter if the connection times out or the database has been deleted, you want to send 'no_data'.

Remember that a union is a single query. Parts of it can't work while other parts fail. It is all or nothing.

select 1
union all
select 1 where 1 = 'x' --this query would fail

Consider the above code. It is a simple query with a union. The second query will cause the whole thing to fail. If you want to capture row counts for each query they need to be run separately. There is no way to know from the results which query in a union returns results.

Perhaps if you can explain the whole process a little more clearly I can see if I can help figure out a way to get what you want.

_______________________________________________________________

Need help? Help us help you.

Read the article at http://www.sqlservercentral.com/articles/Best+Practices/61537/ for best practices on asking questions.

Need to split a string? Try Jeff Moden's splitter.

Cross Tabs and Pivots, Part 1 – Converting Rows to Columns
Cross Tabs and Pivots, Part 2 - Dynamic Cross Tabs

Post #1378470

dwain.c

Posted Tuesday, October 30, 2012 2:23 AM

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eugene.pipko (10/29/2012)

My suggestion:
1. INSERT each of the SELECT FROM view statements into a Temp table.
2. Surround each with a TRY/CATCH.
3. Set a flag in each CATCH to tell you which query failed.
4. SELECT out of the temp table the results that were returned.

No loops! No CURSORs! No RBAR! Hoo-uh!

INDEXing a poor-performing query is like putting sugar on cat food. Yeah, it probably tastes better but are you sure you want to eat it?

Need to UNPIVOT? Why not CROSS APPLY VALUES instead?
Since random numbers are too important to be left to chance, let's generate some!
Are you too recursively challenged?
Splitting strings based on patterns can be fast!

Post #1378609

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