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A Mess of Nested Transactions
Transactions are an area that I often find are used badly, or not used at all. Transactions without any error handling, nested transactions, named transactions named for no good reason or just plain...
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Savepoints and conditional transactions
This is the second in a short series on transactions. In the previous part I discussed nested transactions and showed that they actually don’t exist. SQL has syntax which may suggest that nested...
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Why would you want to name a transaction?
Something that i keep seeing in documentation, in forum code and in real systems is transactions that have names BEGIN TRANSACTION VeryImportantProcess <do stuff> COMMIT VeryImportantProcess Now...
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When naming transactions causes an error
For the last part of the series on transactions, I’m going to look at a problem that I ran across entirely by chance while doing some performance tuning. A procedure had a transaction in it, and it was...
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Does an index scan always read the entire index?
No. That’s a bit short for a blog post, so let me explain. First, the difference between a seek and a scan. A seek is an operation which navigates down the index’s b-tree looking for a row or for the...
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On the addition of useless where clauses
I remember a forum thread from a while back. The question was on how to get rid of the index scan that was in the query plan. Now that’s a poor question in the first place, as the scan might not be a...
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and other pointless query rewrites
In a similar vein to last week’s blog post… I heard an interesting comment recently. “Change that Column != 2 to a Column > 2 or Column < 2 combination, it can use indexes better.” Sounds like...
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SQL Server 2016 features: Temporal Tables
Another new feature in SQL 2016 is the Temporal Table (or System Versioning, as its referred to in the documentation). It allows a table to be versioned, in terms of data, and for queries to access...
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What is a SARGable predicate?
‘SARGable’ is a weird term. It gets bandied around a lot when talking about indexes and whether queries can seek on indexes. The term’s an abbreviation, ‘SARG’ stands for Search ARGument, and it means...
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Homebuilt sequential columns
I gave my introductory session on transactions at all three of the South African SQL Saturdays in 2016, as well as at SQL Saturday Oregon in October 2017, and something that came up in most of them was...
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Revisiting catch-all queries
I originally wrote about catch-all queries early in 2009, just as something that I’d seen several times in client code. It turned into the 3rd most popular post ever on my blog. A lot’s changed since...
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No, this is not a bug in T-SQL
(or, Column scope and binding order in subqueries) I keep seeing this in all sorts of places. People getting an unexpected result when working with a subquery, typically an IN subquery, and assuming...
View ArticleIn-line scalar functions in SQL Server 2019
Yes, yes, yes, finally! It’s hardly a secret that I’m not a fan of scalar user-defined functions. I refer to them as ‘developer pit-traps’ due to the amount of times I’ve seen developers absolutely...
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When naming transactions causes an error
For the last part of the series on transactions, I’m going to look at a problem that I ran across entirely by chance while doing some performance tuning. A procedure had a transaction in it, and it was...
View ArticleClik here to view.
Does an index scan always read the entire index?
No. That’s a bit short for a blog post, so let me explain. First, the difference between a seek and a scan. A seek is an operation which navigates down the index’s b-tree looking for a row or for the...
View ArticleClik here to view.
On the addition of useless where clauses
I remember a forum thread from a while back. The question was on how to get rid of the index scan that was in the query plan. Now that’s a poor question in the first place, as the scan might not be a...
View ArticleClik here to view.
and other pointless query rewrites
In a similar vein to last week’s blog post… I heard an interesting comment recently. “Change that Column != 2 to a Column > 2 or Column < 2 combination, it can use indexes better.” Sounds like...
View ArticleClik here to view.
SQL Server 2016 features: Temporal Tables
Another new feature in SQL 2016 is the Temporal Table (or System Versioning, as its referred to in the documentation). It allows a table to be versioned, in terms of data, and for queries to access...
View ArticleClik here to view.
What is a SARGable predicate?
‘SARGable’ is a weird term. It gets bandied around a lot when talking about indexes and whether queries can seek on indexes. The term’s an abbreviation, ‘SARG’ stands for Search ARGument, and it means...
View ArticleClik here to view.
Homebuilt sequential columns
I gave my introductory session on transactions at all three of the South African SQL Saturdays in 2016, as well as at SQL Saturday Oregon in October 2017, and something that came up in most of them was...
View Article