Latest Posts

Four minor new features of SQL 2008

There are a couple of new features of SQl Server 2008 that I’m pretty excited about that I haven’t seen geet agreat amount of attention. I thought I’d write a short article on them, so they don’t get overlooked.

  1. Variable initialisation
  2. Row constructors
  3. Multi-server queries
  4. Intellisense/syntax checking

Variable Initialisation

I’ve always been more partial to the C# way of declaring and initialising variables all at once. Now it’s possible in T-SQL too.

DECLARE @SomeVariable INT = 0, @SomeOtherVariable CHAR(5) = ‘Hello’

It’s not revolutionary, but I do like it. Anything that reduces the amount of typing and reduces the chances of bugs is worthwhile in my opinion

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Dev Chat

I spent yesterday at the JHB SQL Server 2008 Dev Chat. Most definitely a day well spent. The two presenters (Peter Willmot and Eben de Wit) were both knowledgeable and entertaining and the material covered was interesting.

The sessions covered some of the larger changes in SQL Server 2008.

First up was a brief look at some of the changes on the administration side. The first topic was around the transparent database encryption. this is a fantastic feature for people concerned about the security of the database files themselves. The database is encrypted on disk, decrypted in memory, and any attempt to attach the encrypted files to another instance of Sql will fail, unless the certificate that was used to encrypt the database is present on the second instance.

One major warning on that. Loose the certificate, say goodbye to your database.

Second of the admin-related changes discussed was the DMF (Policy-based management). This is a fantastic new feature and there are two nice ways of using it.

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On recoverability

Had a lovely situation this morning.

I can’t go into details, but essentially a database had no off-site backups, no tape backups and the only full backups were on disk. Then the SAN glitched and both the data files and backups were corrupted.

I’m probably preaching to the converted, but I don’t think there are many more important things on a production server than ensuring good backups.

However, having the backups is not enough. Can they be restored? If there’s a complete drive failure of all drives connected to a server, can the databases be recovered?

When the pawpaw hits the fan (as the local saying goes), that’s the only thing that matters.

Parameter sniffing, pt 2

A while back I wrote about parameter sniffing, the situation where SQL compiles and caches an execution plan that is appropriate for a certain value of a parameter, but is non optimal for other values. There’s another side to parameter sniffing though – when the optimiser can’t sniff at all.

When a batch is submitted to the optimiser, the value of any parameters (from stored procedure, auto parametrisation or sp_executesql) are known to the optimiser. So are the value of any constants used in the SQL statement. The value of local variables, however, are not.

When the value of a variable used in the where clause is not known, the optimiser has know idea what value to use to estimate the number of affected rows. Hence, it has no idea how many rows from the table will satisfy the condition.

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Status report

Just a very quick post, so no one thinks I fell off the edge of the planet.

This blog just passed 2000 hits today. Considering the 1000 mark was passed just over a month ago, that’s really, really good. I’m also up to 15 rss readers, which is quite encouraging

On the downside, I’m swamped with real work, work for university,  prep for my roleplaying game and an assortment of other stuff. Hopefully there’ll be a post up by end of week.

RIP Ken Henderson

I just ran across the news now. Oh my.

I attended a presentation that he did at the Pass conference in Denver last year. I was struck by his passion and humility. I have two of his books, and they are for me a first point of reference for any problem.

He will be sorely missed.

Edit: Just ran across a very nice tribute to Ken.

Ken Henderson

Execution plan operations – aggregates

On to aggregates.

I’m not going to dwell too long on the logical operators for aggregates, as they aren’t as interesting as the joins were. Rather I’m going to concentrate on the physical operators involved.

The two physical operators used for aggregates (and a couple of other logical operations) are:

  • Stream Aggregate
  • Hash Aggregate

Stream Aggregate

The stream aggregate is the faster and more efficient of the aggregate operators. For it to be used, the input rowset must be sorted in order of the grouping columns.

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Comparisons with NULL

Or ‘True, False or FileNotFound’ (1)

Null seems to confuse a lot of people. The main issue with null is that it is not a value. It’s the absence of a value, a place holder for unknown data. Hence, when it is used in a comparison, it returns results that look surprising. Take this as a quick example

DECLARE @Var1 INT
SET @Var1 = NULL

SELECT
CASE WHEN @Var1 = NULL THEN ‘Var1 = Null’ ELSE ‘Var1 <> NULL’ END AS EqualityTest,
CASE WHEN @Var1 <> NULL THEN ‘Var1 <> Null’ ELSE ‘Var1 = NULL’ END AS InequalityTest

The results look a little strange. They’re supposed to. (No, I didn’t mean IS NULL/IS NOT NULL)

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SQL 2008 training

I’ve run into a bunch of free SQL Server 2008 training over the last few days.