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.
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 more20 January 2017
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 more27 October 2016
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 more25 August 2016
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 more10 August 2016
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 more22 July 2016
With the formatting of code, we sometimes do things because they've always been done that way, rather than making code easier to understand. Occasionally these habits get in the way of readability. Joe Celko goes deep into his memorybanks to explain how these deep-seated traditions started. … Read more10 May 2016
Views in SQL can be difficult. It isn't easy to judge when to use them, It isn't always obvious how to determine if a view can be indexed or if it is updateable. Joe Celko takes a tricky topic and comes up with some helpful guidelines.… Read more11 April 2016
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 more08 February 2016
It sometimes pays to go back and look at what you think you already know about SQL. Joe Celko gives a quick revision of the GROUP BY and HAVING clauses in SQL that are the bedrock of any sort of analysis of data, and comes up with some nuggets that may not be entirely obvious… Read more13 January 2016
SQL is unusual is that data is not passively stored. Instead you use declarative SQL to specify the rules that underlie the data and its integrity. When used properly, constraints can avoid having to provide a lot of logic elsewhere. CHECK() and DEFAULT can do a lot to ensure that your data is correct… Read more15 December 2015
There are several ingenious ways of using SQL References to enforce integrity declaratively. Declarative Referential Integrity (DRI) is more effective than using procedural code in triggers, procedures or application layers because it uses the SQL paradigm, thereby making optimisation easier and providing clearer expression of the rules underlying the data.… Read more04 December 2015
In SQL, you can express the logic of what you want to accomplish without spelling out the details of how the database should do it. Nowhere is this more powerful than in constraints. SQL is declarative, and Joe Celko demonstrates, in his introduction to Declarative SQL, how you can write portable code that performs well and executes some complex logic, merely by creating unique constraints.… Read more14 July 2015
Although we like to think that our programming techniques are progressive and in tune with the bleeding edge of software development practices, too often they are directly influenced by restrictions faced in the post-war decades when computers
first became mainstream. As these restrictions no longer apply, is it time to relinquish such things as cursors,
'tibbling', storing display formats, using short names for symbols and primary keys?… Read more11 February 2015
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 more06 January 2015
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 more17 October 2014
As a society, we have an unrealistic respect for data, especially if it has a decimal point somewhere and uses metric units. We who are in the business of data need to cultivate a renewed interest in the sceptical and rigorous science of statistics: it is too important to leave to 'Data Scientists'. If the data is wrong, or the way we analyse or report it is misleading, much of what we do is pointless… Read more28 July 2014
It is awkward to do 'Graph databases' in SQL to explore the sort of relationships and memberships in social networks because equivalence relations are classes (a set of sets) rather than sets. However one can explore graphs in SQL if the relationship has all three of the mathematical properties needed for an equivalence relationship. … Read more05 June 2014
Joe finds a reference to Conway's Game of Life whilst clearing out his desk, and is suddenly gripped with nostalgia. It wasn't just flares, mullets and disco, but simple computer games in interpreted basic. Somehow, Conway s Game of Life was too intriguing to be abandoned in the attic. Can it be implemented in SQL? Joe sets up a challenge.… Read more07 April 2014
The calendar is inherently complex by the very nature of the astronomy that underlies the year, and the conflicting historical conventions. The handling of dates in TSQL is even more complex because, when SQL Server was Sybase, it was forced by the lack of prevailing standards in SQL to create its own ways of processing and formatting dates and times. Joe Celko looks forward to a future when it is possible to write standard SQL date-processing code with SQL Server.… Read more
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