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.

08 September 2017
08 September 2017

Missing Data

In the real world of business or scientific reporting and analysis, data can prove to be awkward. It can be plain wrong or it can be altogether missing. Sure, we have the NULL to signify unknown, but that doesn't play well with regular business reporting. There are a number of ways of dealing with missing information, and methods of estimating data from existing data has a long and respectable history. Joe Celko gets to grips with a data topic that is often treated with some trepidation. … Read more
11 August 2017
11 August 2017

Simple SQL: Random Thoughts

How does one get a truly random sample of data of a certain size from a SQL Server database table. Well, there are simple non-portable tricks one can use, such as the NewID() function, but then refining those can be tricky. Take the Rand() function for a start. Can it really provide you with a truly random number? Why doesn't the TABLESAMPLE clause give you a set number of rows? Joe Celko scratches his head a bit, explains some of the issues and invites some suggestions and tricks from readers.… Read more
28 July 2017
28 July 2017

Data in Motion and Data at Rest

Microsoft (StreamInsight), and Azure Stream Analytics represent a very different model for processing data. They are concerned with processing complex event streams of data (CEPs) from such things as sensors to deduce significant patterns and apply filters. Joe Celko discusses the background to an intriguing technology of complex event processing to establish the difference between data at rest, and data on the move.… Read more
17 July 2017
17 July 2017

SQL Data Aggregation Aggravation

When we have to deal with and store a lot of data, it makes sense to aggregate it so that we store only the information we actually need. If we get this right, this works well, but the design of the system takes care and thought because the problems can be subtle and various. Joe Celko describes some of the ways that things can go wrong and end up providing incorrect, inaccurate or misleading results.… Read more
23 May 2017
23 May 2017

Simple SQL: Attribute Splitting

If the design of a relational database is wrong, no amount of clever DML SQL will make it work well. Dr. Codd’s Information Principle is that you have, inside the entity tables, the columns that model the attributes of that entity. The columns contain scalar values. Tables that model relationships can have attributes, but they must have references to entities in the schema. You split those attributes at your peril. Joe Celko explains the basics.… Read more
20 January 2017
20 January 2017

Handling Graphs in SQL

Many practical database problems can be tackled more simply and intuitively by graphs or networks, which in this sense are graphs in which attributes can be associated with the nodes and edges. It is a natural way to study relationships within the data. SQL databases aren't the easiest way of doing it, but it makes sense where the scale permits it. Because of the range of graphs and techniques, some Graph theory is unavoidable before you get stuck into the code, and who better to introduce graph databases than Joe Celko? … Read more
25 August 2016
25 August 2016

Predicates With Subqueries

The ALL, SOME and ANY predicates aren't much used in SQL Server, but they are there. You can use the Exists() predicate instead but the logic is more contorted and difficult to read at a glance. Set-oriented predicates can greatly simplify the answering of many real-life business questions, so it is worth getting familiar with them. Joe Celko explains.… Read more
10 August 2016
10 August 2016

Formatting SQL Code – Part the Second

When you're formatting SQL Code, your objective is to make the code as easy to read with understanding as is possible, in a way that errors stand out. The extra time it takes to write code in an accessible way is far less than the time saved by the poor soul in the future, possibly yourself, when maintaining or enhancing the code. There isn't a single 'best practice, but the general principles, such as being consistent, are well-established. Joe Celko gives his take on a controversial topic.… Read more
11 April 2016
11 April 2016

The Practical Problems of Determining Equality and Equivalence in SQL

In theory, it is easy to determine whether data is equal to, greater than or lesser than a value. Real-world data types can be surprisingly tricky, even for gauging data equivalence. Because SQL cannot remain aloof from any application's data types, you need to be aware of the ways and pitfalls of individual datatypes and how you can test for equality, equivalence, similarity, identity and all that jazz… Read more