Joe Celko is one of the most widely read of all writers about SQL, and was the winner of the DBMS Magazine Reader's Choice Award four consecutive years. He is an independent consultant living in Austin, TX. He has taught SQL in the US, UK, the Nordic countries, South America and Africa.
He served 10 years on ANSI/ISO SQL Standards Committee and contributed to the SQL-89 and SQL-92 Standards.
He has written over 800 columns in the computer trade and academic press, mostly dealing with data and databases. He is the author of eight books on SQL for Morgan-Kaufmann, including the best selling SQL FOR SMARTIES.
Joe is a well-known figure on Newsgroups and Forums, and he is famous for his his dry wit. He is also interested in Science Fiction.
Data Validation in a database is a lot more complex than seeing if a string parameter really is an integer. A commercial world is full of complex rules for sequences of procedures, of fixed or variable lifespans, Warranties, commercial offers and bids. All this requires considerable subtlety to prevent bad data getting in, and if it does, locating and fixing the problem. Joe Celko shows how useful a State transition graph can be, and how essential it can become with the time aspect added.… Read more
Database design simply involves populating a schema with tables that model sets of entities and relationships. A table will contain Columns that model an entity's attributes and contain scalar values. What could go wrong? Plenty, unfortunately, when these simple principles are misunderstood or flouted, and Joe continues to itemise bad design practices that can cause subsequent grief for the application developers.… Read more
You can easily re-factor bad DML code, but if a database design is wrong, you can do little to rescue the problem, even with expert queries. So what constitutes 'wrong RDBMS design? What are these errors that continually crop up? How can you recognise them and fix them? Joe embarks on a new series of articles by identifying a series of bad practices based on the habit of 'splitting' that which shouldn't be split.… Read more
To make progress as a relational Database programmer, you have to think in terms of sets, rather than lists, arrays or sequential data. Until that point, you'll feel the need to pass lists, arrays and the like to functions and procedures. Joe suggests some unusual ways around the difficulty and broods on the power of the VALUES constructor.… Read more
A number of hierarchies and networks are most convenently modelled as binary trees. So what is the best way of representing them in SQL? Joe discards the Nested Set solution in favour of surprisingly efficient solution based on the Binary Heap.… Read more
It distils a great deal of practical experience; the writing of it was a considerable task; It packs in a great deal of information. Alex's book shows how to write robust database applications, and we can all learn from it. We took the book to a critic who never minces his words, and were relieved to find that Joe Celko liked it. … Read more
Joe Celko reveals the winner of his Easter Stumper: the puzzle of designing an apparently simple database to deal with the process of packing eggs into cartons. It wasn't quite as easy as it looked.… Read more
SQL Server accommodates a whole range of programming styles and will even allow you to create code that is wholly procedural. Is a declarative approach inevitably better? Can it be difficult to maintain? Can you avoid the performance problems of procedural code by using triggers? Joe adds some thoughts.… Read more
A lot of the time, the key to making SQL databases perform well is to take a break from the keyboard and rethink the way of approaching the problem; and rethinking in terms of a set-based declarative approach. Joe takes a simple discussion abut a problem with a UDF to illustrate the point that ingrained procedural reflexes can often prevent us from seeing simpler set-based techniques.… Read more
What can we use in SQL instead of E. F. Codd's T theta operators for best-fit? Joe Celko returns with another puzzle that isn't new, in fact it already features "Swedish", "Croatian" and "Colombian" solutions in chapter 17 of Joe's 'SQL for Smarties' book. These were all written before CTEs or the new WINDOW functions. Is there now a better solution? Was there one even then? We leave it to the readers to provide the answer!… Read more
Joe Celko comes back with a puzzle that isn't new, but one where the answer he originally gave now seems archaic: It is a deceptively simple problem, but is it true that the new features of SQL have simplified the solution? We leave it to the readers to provide the answer!
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Joe Celko explores the dangers of muddling correlation and causation, emphasises the importance of determining how likely it is that a correlation has occurred by chance, and gets stuck into calculating correlation coefficients in SQL. Along the way, Joe illustrates the consequences of leaping to the wrong conclusion from correlations with tales of Pop Dread. … Read more
Joe becomes intrigued by the way that experts make errors in any area of technology, and suggests that the problem is more that of mindsets than lack of knowledge. He illustrates the point with SQL Development by means of the "Britney Spears, Automobiles and Squids" table, and the tangled Stored procedure, and shows ways of getting rid of both procedural and non-procedural code by adopting a different programming mindset.… Read more
Joe Celko kicks off our series of Summer SQL Stumpers with a challenge to improve on his solution to calculating the prime numbers between 1 and 10000. Once the various solutions have been contributed and judged, the winner will be announced. The competition will be run on Simple-Talk and SQL Server Central together.
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A forum posting, from someone who wanted a better solution to the common problem of handling global settings in a database, leads Joe Celko into a fascinating discussion of the ramifications of the various solutions. … Read more
The whole subject of the Three-Valued (also known as ternary, trivalent or 3VL) Logic of SQL tends to trip people up. This is hardly surprising in view of the fact that it involves an esoteric Polish mathematician and because it behaves differently in the DDL (Data Declaration Language) and the DML (Data Manipulation Language). In response to requests, Joe Celko comes to the rescue and makes it all seem simple.… Read more
SQL Server database engine doesn't have a MEDIAN() aggregate function. This is probably because there are several types of median, such as statistical, financial or vector medians. Calculating Medians are essentially a row-positioning task, since medians are the middle value of an ordered result. Easy to do in SQL? Nope. Joe Celko explains why… Read more
Businesses often require reports that require more than the classic set operators. Surprisingly, a business requirement can often be expressed neatly in terms of the DIVISION relationship operator: How can this be done with SQL Server? Joe Celko opens up the 'Manga Guide to Databases', meets the Database Fairy, and is inspired to explain DIVISION.… Read more
In the first part of this series on Temporal Data, Joe explained how it is that the Common Era calendar is irregular and mentioned that, although there are ANSI/ISO Standards for temporal operations in SQL, every vendor has something different. Now, he discusses other factors to take into account when using temporal data such as Holidays, and discusses a few techniques using Calendar, Report Usage and History tables… Read more
In the first of a series of articles on the tricks of tackling temporal data in SQL, Joe Celko discusses SQL's temporal data types and agonizes over the fact that, although there are ANSI/ISO Standards for temporal operations in SQL, every vendor has something different. He explains the mysteries of such things as time-zones, lawful time, UTC, CUT, GMT, CE, DST, and EST.… Read more