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.
The logic for referential integrity can be implemented in application code, but to make sure that it is enforced, include foreign key constraints in the database design instead. In this article, Joe Celko talks about the history of references in SQL and the options available today. … Read more
Understanding scoping rules is a basic skill for developers. In this article, Joe Celko gives a bit of the history of scoping in early programming languages and shows how scoping applies to SQL queries as well. … Read more
There are those who argue that time doesn’t really exist; it’s just an illusion. That debate won’t keep you from storing and manipulating dates and time in SQL Server. In this article, Joe Celko discusses some of the many ways that SQL Server treats temporal data types.… Read more
Whether or not to have NULLable columns in a table can be a religious debate, and how missing data is represented should be carefully considered during database design. In this article, Joe Celko considers the ways that SQL Server handles NULLs in several situations. … Read more
Joe Celko reminisces about the origins of databases and one of the early pioneers, Charles Bachman. He explains how pointer chains were used to traverse data in the NDL standard and referential integrity that we use today.… Read more
Technology is constantly moving forward, but it is also helpful to understand how we arrived where we are today. Joe Celko reminisces about the history of database design and how it relates to the concept of ‘Degree of Duplication’ in this article.… Read more
A proper database design is very important, and changes to fix problems after the fact are expensive. In this article, Joe Celko discusses three aspects of database design that are often overlooked: validation, verification, and modification.… Read more
How do you record locations in SQL? Most relational database systems support spatial and geographical data, generally using the round-earth system based on the SQL specification of the Open Geospatial Consortium (OGC). However, this is not the only approach, as Joe Celko explains. … Read more
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
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
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
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
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
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
Triggers are generally over-used in SQL Server. They are only rarely necessary, can cause performance issues, and are tricky to maintain If you use them, it is best to keep them simple, and have only one operation per trigger. Joe Celko describes a feature of SQL that 'gets complicated fast'.… Read more
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