Articles tagged

28 May 2015
28 May 2015

How to Get SQL Server Dates and Times Horribly Wrong

One of the times that you need things to go right is when you are doing analysis and reporting. This is generally based on time and date. A sure-fire way of getting managers upset is to get the figures horribly wrong by messing up the way that you handle datetime values in SQL Server. In the interests of peace, harmony and a long career in BI, Robert Sheldon outlines some of the worst mistakes you can make when using SQL Server dates.… Read more
18 May 2015
18 May 2015

Using the T-SQL PERCENTILE Analytic Functions in SQL Server 2000, 2005 and 2008

Percentiles give meaning to measurements by telling you the percentage of the population being measured who get higher or lower values. They are now easier to calculate in SQL, and are useful for reporting; but are the new analytic functions faster and more efficient than the older methods? Dwain Camps demonstrates, and investigates their relative performance performance.… Read more
08 May 2015
08 May 2015

Optimizing Batch Process in SQL Server

SQL Server batch processes are usually run from SQL Agent in background. They can take significant time and resources, especially if they are ETL tasks. Quite often, the responsibility for creating these tasks belongs entirely to the developer. Dennes demonstrates that DBAs can advise and assist with this type of batch job by bringing their expertise to bear on the problem of reducing their impact on the working system to a minimum.… Read more
06 May 2015
06 May 2015

Documenting your SQL Server Database

One of the shocks that a developer can get when starting to program in T-SQL is that there is no simple way of generating documentation for routines, structures and interfaces, in the way that Javadocs or Doxygen provides. To embed the documentation in the source is so obvious and easy that it is a wrench to be without this facility. Phil Factor suggests a solution. … Read more
22 April 2015
22 April 2015

Time Slots – An Essential Extension to Calendar Tables

After answering many forum entries from developers asking for help with dealing with SQL that involved time intervals and ranges, Dwain dreamed of a generalized tool that sets up time slots of various sorts without the need to experiment; that could do the heavy lifting, so that developers could do aggregations and reports based on time intervals without the hard graft. Here is Dwain's dream made reality. … Read more
02 April 2015
02 April 2015

How to Get SQL Server Data-Conversion Horribly Wrong

One of the most certain ways of going wrong with any relational database is to get data conversion wrong. Implicit data conversion is a good feature for the expert but can cause a lot of trouble to the unwary. These boil down to seven ways of failing to get data conversion right. Rob Sheldon explains and gives sage advice on how to avoid the problems… Read more
18 March 2015
18 March 2015

SQL Server Spatial Indexes

Spatial Data in SQL Server has special indexing because it has to perform specialised functions. It is able, for example, to break down an indexed space into a grid hierarchy by using a technique called tessellation. This is a rules-based system that, when you compare a shape to an index, works out how many cells in the the grid hierarchy are touched by that shape , and how deep down the grid hierarchy to search. There is powerful magic in Spatial Indexes as Surenda and Roy explain.… Read more
18 March 2015
18 March 2015

Introduction to SQL Server Spatial Data

More and more applications require the handling of geospatial data. It is easy to store spatial data, but it takes rather more thought to retrieve and manipulate it. Tasks like searching neighborhoods, and calculating distances between points is often required from databases. But how do you start? Roy and Surenda take you through the basics. … Read more
10 March 2015
10 March 2015

Self-maintaining, Contiguous Effective Dates in Temporal Tables

'Temporal' tables contain facts that are valid for a period of time. When they are used for financial information they have to be very well constrained to prevent errors getting in and causing incorrect reporting. This makes them more difficult to maintain. Is it possible to have both the stringent constraints and simple CRUD operations? Well, yes. Dwain Camps patiently explains the whole process.… Read more
27 February 2015
27 February 2015

Defusing Database Time Bombs: Avoiding the Need to Refactor Databases

Where applications are evolved by gradually molding them to a growing understanding of the business domain, this presents great challenges to database development. If databases are designed too loosely, and initial errors are allowed to fester, the results become harder and harder to refactor until eventually they constitute a database time bomb. Thomas LeBlanc describes how to avoid a few basic, but very common, database time bombs. … Read more
11 February 2015
11 February 2015

The DRI Subject of References

A database must be able to maintain and enforce the business rules and relationships in data in order to maintain the data model. It does this through referential constraints. They aren't complex, but are powerful, especially with the means to attach DRI actions to them. Joe Celko explains all, and pines for the ANSI CREATE ASSERTION statement… Read more
11 February 2015
11 February 2015

Checking the Plan Cache Warnings for a SQL Server Database

How often do you check your query plans during development to see if they contain any warnings? If you're missing them, it means that you're not getting all those hints about missing indexes, join predicates or statistics. Is the query optimiser trying to tell you about implicit conversions? Dennes shows how to view the warnings in plan cache for a particular database using SQL… Read more
26 January 2015
26 January 2015

Bowled Over by SQL Window Functions

What better way to learn how to construct complex CHECK CONSTRAINTs, use the SQL 2012 window frame capability of the OVER clause and LEAD analytic function, as well as how to pivot rows into columns using a crosstab query? Create the SQL code to score Ten-pin Bowling, of course. Dwain Camps explains the how, what and why.… Read more
26 January 2015
26 January 2015

Questions About T-SQL Control-of-Flow Language You Were Too Shy to Ask

Surely, we all know how T-SQL Control-of-flow language works? In fact it is surprisingly easy to get caught out. What, for example, do the BREAK, RETURN and CONTINUE keywords do, precisely, in their various contexts? the answers to this and other questions aren't all entirely obvious, but we're too shy to ask them in public, and risk displaying our ignorance.… Read more
06 January 2015
06 January 2015

Discrete and Continuous data in SQL

Not all data is discrete; some data types represent a continuum. In SQL, we have to approximate them and live with the special problems of handling continuous data. We need to understand the problems associated with continuous data types, when these will happen, and how it affects constraints and the results of queries. Joe Celko explains.… Read more
01 January 2015
01 January 2015

Questions About Pivoting Data in SQL Server You Were Too Shy to Ask

Of all the basic SQL operations, the pivot seems to cause the most problems. We can tell from the way that old articles on Simple-Talk on the topic continue to be read. It turns out that there are several questions that come to mind while learning about pivoting, but which are seldom asked on forums. Once more, Robert Sheldon attempts to answer these unspoken questions.… Read more
30 December 2014
30 December 2014

Archiving Hierarchical, Deleted Transactions Using XML

When you delete a business transaction from the database, there are times when you might want to keep a record of the data for posterity. This can become somewhat complicated if the transaction you need to delete is in a table that is the parent of a deeply nested hierarchy of dependent tables based on the foreign key relationships. In this article, Dwain Camps looks at a tidy means of doing just that.… Read more
04 December 2014
04 December 2014

Questions About T-SQL Transaction Isolation Levels You Were Too Shy to Ask

Every time you access a relational database to make a query, you have an important decision to make: What is the appropriate isolation level for your query? If you get this wrong, the consequences can be serious. Deadlocks, Dirty reads, Non-repeatable reads, or poor performance. We're in luck, because Robert Sheldon once more answers those questions that are awkward to ask in public.… Read more
18 November 2014
18 November 2014

Bitwise Operations in T-SQL

How can you, in T-SQL, get a list of columns that have changed within a trigger? How can you see what bits are set within a varbinary or integer? How would you pass a bitmap parameter to a system stored procedure? Phil Factor shows how, introduces the bitwise operations, illustrates ways of peeking at bit-level operations, and explains the concepts behind the coding of integer datatypes.… Read more