I have a stored procedure which queries in 5 secs.
Recently i have added a UDF in select
select col1,col2,col3,UDF_function(col1),col4 from table inner join table 1 ..........11 tables are joined here.
after adding udf_function() my query execution time is taking minimum 15 mins which is horrible. Kindly help me to how to improve the performance.
the function returns the values of a column as comma seperated string. it means i am looping through the records in the function.
The reason why i am using UDF is becos of the below table structure and requirement
p.k col1 col2 col3 1 x z 2 v q 3 n w 4 m e
f.k 1 a 1 b 1 c 2 a 2 d
col1 col2 1 a,b,c 2 a,d 3 4
This is mainly to avoid duplicates
Thanks in advance Usha
You could try creating an indexed view based off the UDF for pre-aggregation. Go to BOL and search on Creating Indexed Views
Based on your new information I would say you could create an indexed view utilizing the UDF for every table.
The views would basically be
You would then have persisted data and could join this into your query.
Assuming the views created column one as the FK and column two as the comma separated list you could do something similar to the following:
I suspect your problem is that you're falling into Jeff Moden's RBAR (Row By Agonising Row). What you're attempting to do should be possible with an appropriate aggregate.
answered Nov 03 '09 at 08:58 AM
Melvyn Harbour 1 ♦♦
You probably want to read this blog post http://sqlblog.com/blogs/adam_machanic/archive/2009/05/31/grouped-string-concatenation-the-winner-is.aspx
It is all about how to return grouped strings. There is an attached file which contains the winning scripts. Look at them to see what can be done with this matter.
answered Nov 03 '09 at 09:38 AM
Also, bear in mind that calling any sort of scalar UDF on a row-by-row basis can dramatically reduce performance.
answered Nov 03 '09 at 09:42 AM
Matt Whitfield ♦♦
Im not clear behind your reasons for doing this.
You say "This is mainly to avoid duplicates" surely, is that you want the distinct characters in the columns ?
Please provide a better example , as SQL script would be perfect
answered Nov 04 '09 at 05:47 AM