Joe Celko

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.

15 February 2010
15 February 2010

Procedural, Semi-Procedural and Declarative Programming in SQL

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
19 January 2010
19 January 2010

Celko’s SQL Stumper: The Class Scheduling Problem

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
15 September 2009
15 September 2009

Causation, Correlation and Crackpots

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
20 August 2009
20 August 2009

Getting rid of SQL Code

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
07 May 2009
07 May 2009

SQL and the Snare of Three-Valued Logic

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
05 April 2009
05 April 2009

Median Workbench

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
17 February 2009
17 February 2009

Divided We Stand: The SQL of Relational Division

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
18 January 2009
18 January 2009

Temporal Data Techniques in SQL

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
16 December 2008
16 December 2008

Temporal Datatypes in SQL Server

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
26 October 2008
26 October 2008

Constraint Yourself!

In his first article for Simple-Talk, Joe Celko demystifies the use of Constraints, and points out that they are an intrinsic part of SQL and are a great way of ensuring that a business rule is done one way, one place, one time. Almost all database programmers will find something new and useful in this article.… Read more