T-SQL Queries Archives - Page 15 of 17

If you are using indexed views and MERGE, please read this!

Here is some information about an important MERGE "wrong results" bug, involving indexed views, that could be affecting the accuracy of your queries right now, and what options you have for working around the problem.

Aaron Bertrand ◆ February 6, 2013

6

Generate a set or sequence without loops – part 3

Earlier in this series (Part 1 | Part 2) we talked about generating a series of numbers using various techniques. While interesting, and useful in some scenarios, a more practical application is to generate a series of contiguous dates; for example, a report that requires showing all the days of a month, even if some days had no transactions.

Aaron Bertrand ◆ January 18, 2013

5

Generate a set or sequence without loops – part 2

In my previous post, I talked about ways to generate a sequence of contiguous numbers from 1 to 1,000. Now I'd like to talk about the next levels of scale: generating sets of 50,000 and 1,000,000 numbers.

Aaron Bertrand ◆ January 17, 2013

8

Generate a set or sequence without loops – part 1

There are many use cases for generating a sequence of values in SQL Server. I'm not talking about a persisted IDENTITY column (or the new SEQUENCE in SQL Server 2012), but rather a transient set to be used only for the lifetime of a query. Or even the simplest cases – such as just appending a row number to each row in a resultset – which might involve adding a ROW_NUMBER() function to the query (or, better yet, in the presentation tier, which has to loop through the results row-by-row anyway).

Aaron Bertrand ◆ January 16, 2013

14

Potential enhancements to ASPState

Many people have implemented ASPState in their environment. Some people use the in-memory option (InProc), but usually I see the database option being used. There are some potential inefficiencies here that you might not notice on low volume sites but that will start to affect performance as your web volume ramps up.

Aaron Bertrand ◆ January 11, 2013

14

Should I use NOT IN, OUTER APPLY, LEFT OUTER JOIN, EXCEPT, or NOT EXISTS?

SQL Sentry's Aaron Bertrand (@AaronBertrand) digs into the left anti semi join, comparing NOT IN, NOT EXISTS, OUTER APPLY, EXCEPT, and OUTER JOIN methods.

Aaron Bertrand ◆ December 27, 2012

27

TRANSACTION_MUTEX and Multi-Session Transaction Access

I recently encountered high TRANSACTION_MUTEX accumulated wait time on a client system. I couldn’t recall a case where I saw this wait type as near the top of the “high waits” list and I was curious about what factors could push this type of overall wait time.

The Books Online definition of TRANSACTION_MUTEX is that it "occurs during synchronization of access to a transaction by multiple batches." Not many areas within the SQL Server engine expose this type of functionality, so my investigation was narrowed down to the following technologies:

Joe Sack ◆ December 10, 2012

6

The Benefits of Indexing Foreign Keys

Primary and foreign keys are fundamental characteristics of relational databases, as originally noted in E.F. Codd’s paper, “A Relational Model of Data for Large Shared Data Banks”, published in 1970. The quote often repeated is, "The key, the whole key, and nothing but the key, so help me Codd."

In this post, Erin Stellato (@erinstellato) discusses the benefits of adding indexes on top of declared referential constraints.

Erin Stellato ◆ November 20, 2012

16

Ten Common Threats to Execution Plan Quality

The quality of an execution plan is highly dependent on the accuracy of the estimated number of rows output by each plan operator. If the estimated number of rows is significantly skewed from the actual number of rows, this can have a significant impact on the quality of a query's execution plan. Poor plan quality can be responsible for excessive I/O, inflated CPU, memory pressure, decreased throughput and reduced overall concurrency.

Joe Sack ◆ November 13, 2012

11

Bad cardinality estimates coming from SSMS execution plans

I have a few people to thank for a recent update to Plan Explorer. Brooke Philpott (@Macromullet) and Greg Gonzalez (blog | @SQLsensei), of course, for R & D and for digging into the code and sorting it out. But also to Paul White for being persistent in helping us validate the fixes.

Aaron Bertrand ◆ November 2, 2012

0

Beware misleading data from SET STATISTICS IO

My co-worker Steve Wright (blog | @SQL_Steve) prodded me with a question recently on a strange result he was seeing. In order to test some functionality in our latest tool, SQL Sentry Plan Explorer PRO, he had manufactured a wide and large table, and was running a variety of queries against it. In one case he was returning a lot of data, but STATISTICS IO was showing that very few reads were taking place.

Aaron Bertrand ◆ October 30, 2012

11