24Apr 2009 by Grant Fritchey 15 Comments

Unpacking the View

SQL Server, T-SQL
A view is simply a query that behaves something like a table. Most people know this. Most people also know that a view is simply a mask on top of what might be a very complex query. It all seems really simple. You call the view inside a simple query, the view runs the underlying complex query. Most people might not know that when a view is called and it gets sent to the optimizer, the optimizer unpacks the view and binds the component parts of the query necessary to create an execution plan that will return the data requested. What I didn't know until recently was that the optimizer is VERY smart. Not only does it unpack the query of the view, but it will change the query that…
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13Apr 2009 by Grant Fritchey 4 Comments

Paul Randal’s Database Size Survey

SQL Server, T-SQL
If you have three minutes to spare, swing by Paul Randal's blog and answer his survey questions about the size and distribution of your database. The results are very interesting. I was most interested in the number of respondents to each of the questions.  As each size category switched, fewer and fewer people responded. However, a lot more people responded than I expected. 94 last I looked had databases under 10gb in size, but 42 had databases over 1tb. Yeah, that's only 1/2, but, holy cow, it's 1/2. I wish I had a database to manage that was over 1tb. Back in the 7.0/2000 days I was at a dot com that was getting close. When I left they had 700gb. I understand they got close to 850 before the…
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07Apr 2009 by Grant Fritchey 3 Comments

SQL Server Standard Article Available

PASS, SQL Server, T-SQL
Unfortunately PASS decided to put the SQL Server Standard to sleep right after I got an article published in it (and no, it wasn't my fault). However, PASS, being the service oriented organization that they are, has decided to make back issues of the magazine available online. So, to read the article I wrote comparing various methods of retrieving versioned data using different TSQL constructs, click this link. Go to page 14. Oh yeah, and you can see other peoples articles here too. There are other things coming out of the editorial committee soon (although I need to get one of them done myself... yikes).
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07Apr 2009 by Grant Fritchey 6 Comments

NULL Is Not NULL

SQL Server, T-SQL
NULL as a concept seems so easy but it leads to so many problems for people. To put it as simply as possible, NULL does not equal anything. It does not "not equal" anything either. It can't be compared to other values in any way. There was a recent post over at SQL Server Central where the user had a query problem that one of the great people over at SSC solved, handily. They also pointed out that the bit of code being used "WHERE nt.NullableString NOT LIKE 'null%'" was also a problem. The user insisted that it was eliminating the NULL values. Well, yeah, sort of, it was, but not because it was actually applying a filter to the NULLs. Remember, a NULL does not equal or "not equal"…
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26Mar 2009 by Grant Fritchey No Comments

INNER JOIN Experiment in Order

SQL Server, T-SQL
And a new blog. Christopher Stobbs, one of the frequent posters over at SSC decided to try his hand at blogging. His first post is up and it's pretty interesting. He ran an experiment with all different orders of tables, largest to smallest, smallest to largest to see if the order in the joins made a difference. For the answer, click
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04Mar 2009 by Grant Fritchey 7 Comments

Bad Performance Tip

SQL Server, T-SQL
I saw a performance tip that just didn't make any sense to me: In cases where you are using the IN clause, try to order the list of values so that the most frequently found values are placed first. That just didn't make any sense to me. The IN clause is not like EXISTS where the query will stop as soon as it finds a good match. So I set up a test with AdventureWorks. I found a few different ProductId values, the highest, the lowest and a few in between and ran a very simple query to test this tip: /* ProductID        RowCount 870                        4688 rows 877                        1327 rows 972                        380 rows 823                        148 rows 723                        52 rows 897                        2 rows*/ DBCC FReeproccache() DBCC dropcleanbuffers() GO SELECT  sod.ProductID        ,sod.SalesOrderDetailID FROM    Sales.SalesOrderDetail AS sod WHERE   sod.ProductID IN (870, 877,…
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02Mar 2009 by Grant Fritchey 9 Comments

More Refinements on the Missing Indexes Query

SQL Server, T-SQL
Greg Larson posted a really nice query to find worst performing stored procedures in your system. He put in all kinds of attributes to make it customizable, changing the definition of "worst" to different measures,etc. Great query in general. In it he linked to sys.dm_exec_plan_attributes and got the db_id attribute. Duh! So instead of spelunking through the XML to retrieve the database name, I can pull the db_id and use the DB_NAME function. Cleans things up considerably. Thanks Greg. Here's the cleaned up code: WITH XMLNAMESPACES ('http://schemas.microsoft.com/sqlserver/2004/07/showplan' AS sp) SELECT DB_NAME(CAST(pa.value AS INT)) ,s.sql_handle ,s.total_elapsed_time ,s.last_execution_time ,s.execution_count ,s.total_logical_writes ,s.total_logical_reads ,s.min_elapsed_time ,s.max_elapsed_time --,s.query_hash ,p.query_plan ,p.query_plan.value(N'(sp:ShowPlanXML/sp:BatchSequence/sp:Batch/sp:Statements/sp:StmtSimple/sp:QueryPlan/sp:MissingIndexes/sp:MissingIndexGroup/sp:MissingIndex/@Table)[1]', 'NVARCHAR(256)') AS TableName ,p.query_plan.value(N'(/sp:ShowPlanXML/sp:BatchSequence/sp:Batch/sp:Statements/sp:StmtSimple/sp:QueryPlan/sp:MissingIndexes/sp:MissingIndexGroup/sp:MissingIndex/@Schema)[1]', 'NVARCHAR(256)') AS SchemaName ,p.query_plan.value(N'(/sp:ShowPlanXML/sp:BatchSequence/sp:Batch/sp:Statements/sp:StmtSimple/sp:QueryPlan/sp:MissingIndexes/sp:MissingIndexGroup/@Impact)[1]', 'DECIMAL(6,4)') AS ProjectedImpact ,ColumnGroup.value('./@Usage', 'NVARCHAR(256)') AS ColumnGroupUsage ,ColumnGroupColumn.value('./@Name', 'NVARCHAR(256)') AS ColumnName FROM (SELECT TOP 20 s.sql_handle ,s.plan_handle ,s.total_elapsed_time…
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26Feb 2009 by Grant Fritchey No Comments

Shrinking Databases

SQL Server
Tim Ford put up a hilarious blog post outlining an instance where shrinking databases is acceptable. I'm pretty sure the development method he describes is well documented and in use in more than one location around the world, including somewhere in my company. Read it.
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25Feb 2009 by Grant Fritchey No Comments

Three Kinds of Execution Plans

SQL Server, T-SQL
You read that correctly, three kinds of execution plans. You may have thought that all you had to deal with are estimated and actual, but there is one more. The estimated plan is the plan that comes out of the optimizer. It's based on statistics and indexes and known objects within the system. The actual plan is the plan that was used to execute the query and will show all the actual number of rows processed, etc. It might be different than the estimated plan because the stastics were off or for any number of other reasons. Those were the ones you knew about. There is also the plan that gets stored in the plan cache, the compiled plan. I lied. The compiled plan and the estimated plan are the…
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