The SQL Dude! Well, this post has been due for quite some time. I had opened up a survey/opinion poll on https: //thesqldude. No schema changes have been made though its quite possible data changes have been happening. The update query goes like this,update msgboard set mb. At this point, two questions should pop into your head. Why is the query using the clustered index? Why is it performing a Scan operation? Answer to question #1. Let’s look at the update query carefully. The query is updating the columns mb. You might think, well, I have an index IX. The query looks like this,update msgboard set mb. It does because, the statistics for this NC index would be built on the leading column which is mb. Here is how the histogram looks. If SQL Server were to use the NC index, it would be do a lookup or cache the results (ahem, Table Spool operator!) and then find the matching row in the clustered index to actually update the 2 columns. This is an additional cost, and this is why SQL decided not to go with this plan. Coming to the 2nd question of why a Scan? It might surprise some of you, but a Seek does not imply good performance always. My favourite answer – “It depends”. Have you ever needed to write some code that would process through all the tables in a database? What about running some code against each database on a SQL Server instance? If so, did you know there are a couple of. When I asked a friend from the SQL Server development team “what’s the story behind Logon Triggers?” the answer was brief “Common Criteria compliance for SQL Server and nothing more”. That is, indeed, the short story. Launch SSMS and open a query window. Look at the lower right, you should see you're logged with your domain login. Right click the query screen, choose the 'Connection' option, and then 'Change Connection. Today, the reverse with the power designer mysql database and found that actually can not establish 192.168.1.22 mysql odbc data source, reports: Connection Fialed: Every SharePoint admin is likely to do one thing at least one time in their career: Move databases to a new SQL Server or instance. I was lucky enough to get to do it again, most recently, overnight tonight for a customer, so. System Center Configuration Manager sccm 2012, sccm 2007, ConfigMGR 2012, ConfigMGR 2007, System Center Configuration Manager. Major life changes recently! Here’s the summary: I left Skyline in December 2015; I moved to Austin, TX in December 2015; I started at Microsoft in January 2016; It’s been a hectic year.so needless to say I haven’t been. In this case, the table only had 1. When using the CI Scan, SQL Server was applying the filter on mb. A Clustered Index Seek in this case would not make any positive difference in query execution time. OBJECT: (. Based on the query design, if the column being updated mb. In this case that was also also take care of, since IX. This is an important thing and this was why the “included columns” feature was introduced. So, I modified the index IX. Instead, I added the column back as an included column. DROP INDEX . The base table or clustered index data is not accessed resulting in fewer disk I/O operations and hence faster query execution. Also, the index size is lesser since non- key columns are only added to the leaf level. Many advantages indeed. Here is how the update query plan looked after added mb. The actual cost is now 0. So we have achieved our original goals of a) Getting SQL Server to use the Non- clustered index IX. For more information on guidelines and restriction with included columns refer this MSDN article. That’s all for now folks. Keep tuned to this site for more.- The. SQLDude (Sudarshan).
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