Tuning UPDATE query

• WhiteLotus

  SSChampion

  Points: 12122

  More actions

  June 2, 2016 at 12:02 am

  #314351

  Hi Guys ,

  I am tuning an UPDATE query by adding an index

  UPDATE XYZ

  SET Count = Count + 1,

  LastOccured = GetDate()

  WHERE AppID = @AppID

  AND SubString(Message, 1, 50) = SubString(@Message, 1, 50)

  AND DateDiff(mi, CreatedDate, GETDATE()) < 60

  Since it is UPDATE statement that will change the table value I am worried if I run that script to compare before and after I apply Index , it will change the value . If it is SELECT statement I won’t worry ..

  I want to measure the performance by using :

  Set statistics IO on

  So I can analyse the Logical read

  Please kindly advise ..

  Thank you

• ChrisM@Work

  SSC Guru

  Points: 186127

  More actions

  June 2, 2016 at 4:27 am

  #1882765

  WhiteLotus (6/2/2016)

  ---

  Hi Guys ,

  I am tuning an UPDATE query by adding an index

  UPDATE XYZ

  SET Count = Count + 1,

  LastOccured = GetDate()

  WHERE AppID = @AppID

  AND SubString(Message, 1, 50) = SubString(@Message, 1, 50)

  AND DateDiff(mi, CreatedDate, GETDATE()) < 60

  Since it is UPDATE statement that will change the table value I am worried if I run that script to compare before and after I apply Index , it will change the value . If it is SELECT statement I won’t worry ..

  I want to measure the performance by using :

  Set statistics IO on

  So I can analyse the Logical read

  Please kindly advise ..

  Thank you

  An index on anything other than [Appid] won't help much with this query as it stands - functions around columns in the WHERE clause almost always obstruct index usage. Try removing the functions, something like this:

  UPDATE XYZ SET

  [Count] = [Count] + 1,

  LastOccured = GETDATE()

  WHERE AppID = @AppID

  AND CreatedDate >= DATEADD(MINUTE,-90,GETDATE())

  AND [Message] LIKE LEFT(@Message, 50) + '%'

  An index on AppID, CreatedDate and INCLUDEing Message should do it.

  ^{“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