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  • Monitoring skew in PDW

    When you have data stored across several servers, skew becomes very significant. In SQL Server Parallel Data Warehouse (PDW), part of the Analytics Platform System (APS), data is stored in one of two ways – distributed or replicated. Replicated data is copied in full across every compute node (those servers which actually store user data), while ...
    Posted to Rob Farley (Weblog) by rob_farley on May 11, 2015
  • SHOWPLAN permission denied even if the database isn’t actually used

    To view a query plan, you need SHOWPLAN permission on the database level at least. You have this if you have CONTROL DATABASE, or CONTROL SERVER, or if you have ALTER TRACE at the instance level. I know this last one because it’s mentioned in Books Online on the ‘Database Permissions’ page, not because it’s particularly intuitive. As a ...
    Posted to Rob Farley (Weblog) by rob_farley on April 14, 2015
  • Tuning Parallel Data Warehouse Queries

    Performance tuning in regular SQL Server can be addressed in a number of ways. This can involve looking at what’s going on with the disk configuration, the memory configuration, the wait stats, the parallelism settings, indexing, and so much more. But if you have a Parallel Data Warehouse (PDW) environment, then there are a lot of things that are ...
    Posted to Rob Farley (Weblog) by rob_farley on March 9, 2015
  • SQL Injection – the golden rule

    The problem with SQL Injection is that most people don’t realise the fundamental concept which makes SQL Injection vulnerability not only easy to spot, but also easy to prevent. And it’s the thing that SQL Injection has in common with countless other hacking mechanisms that have been around since the early days of computing. The simple truth is ...
    Posted to Rob Farley (Weblog) by rob_farley on February 9, 2015
  • SSIS Lookup transformation in T-SQL

    There is no equivalent to the SSIS Lookup transformation in T-SQL – but there is a workaround if you’re careful. The big issue that you face is about the number of rows that you connect to in the Lookup. SQL Books Online (BOL) says: If there is no matching entry in the reference dataset, no join occurs. By default, the Lookup transformation ...
    Posted to Rob Farley (Weblog) by rob_farley on July 8, 2014
  • SQL 2014 does data the way developers want

    A post I’ve been meaning to write for a while, good that it fits with this month’s T-SQL Tuesday, hosted by Joey D’Antoni (@jdanton) Ever since I got into databases, I’ve been a fan. I studied Pure Maths at university (as well as Computer Science), and am very comfortable with Set Theory, which undergirds relational database concepts. But I’ve ...
    Posted to Rob Farley (Weblog) by rob_farley on June 9, 2014
  • Tricks in T-SQL and SSAS

    This past weekend saw the first SQL Saturday in Melbourne. Numbers were good – there were about 300 people registered, and the attendance rate seemed high (though I didn’t find out the actual numbers). Looking around during the keynote, I didn’t see many empty seats in the room, and I knew there were 300 seats, plus people continued to arrive as ...
    Posted to Rob Farley (Weblog) by rob_farley on April 7, 2014
  • Scans are better than Seeks. Really.

    There are quite a few reasons why an Index Scan is better than an Index Seek in the world of SQL Server. And yet we see lots of advice saying that Scans are bad and Seeks are good. Let’s explore why. Michael Swart (@MJSwart) is hosting T-SQL Tuesday this month, and wants people to argue against a popular opinion. Those who know me and have heard ...
    Posted to Rob Farley (Weblog) by rob_farley on March 11, 2014
  • Victims of success

    I feel like every database project has major decisions now, which are remarkably fundamental to the direction that’s going to be taken. And it’s almost as if new options appear with ever-increasing frequently. Consider a typical database project, involving a transactional system to support an application, with extracts into a data warehouse ...
    Posted to Rob Farley (Weblog) by rob_farley on February 10, 2014
  • Waiting, waiting…

    “It just runs slow these days” I’m sure you’ve heard this, or even said it, about a computer that’s a few years old. We remember the days when the computer was new, and it seemed to just fly – but that was then, and this is now. Change happens, things erode, and become slower. Cars, people, computers. I can accept that cars get slower. They lose ...
    Posted to Rob Farley (Weblog) by rob_farley on December 9, 2013
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