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.
A Dominoes game of Texas 42 inspires Joe to explore unusual uses for check constraints and views. Sometimes, the best way of discovering useful SQL techniques is to tackle the more unusual problems.… Read more
Parts explosions present a classic IT problem. How can one calculate such things as weight or cost of assemblies in SQL? Joe shows how it can be done using nested sets, with not an IDENTITY or GUID in sight..… Read more
It should be easy to model a game of poker in SQL. The problem is, however, that you need to model a permutation from a set of elements. Joe Celko argues that using a group of columns to do this isn't necessarily a violation of 1NF, since a permutation is atomic. Then comes the second problem: how would you sort such a column-base permutation in order? Sorting columns in SQL?… Read more
SQL and Relational Theory, by Chris Date, isn't likely to be a book that SQL's greatest defender, Joe Celko, would agree with. However, following the debates between Date and Celko on the relational purity of SQL has all the fascination of watching Godzilla wrestling King Kong.… Read more
Relational Databases have tables as data structures, not arrays. This makes it tricky and slow to do matrix operations, but it doesn't mean it is impossible to do. Joe gives the Celko Slant on how to go about doing Matrix Math in SQL.… Read more
Following up from his popular article, SQL View Basics, Joe delves into the main uses of views, explains how the WITH CHECK OPTION works, and demonstrates how the INSTEAD OF trigger can be used in those cases where views cannot be updatable.… Read more
SQL Views are essential for the database developer. However, it is common to see them misused, or neglected. Joe Celko tackles an introduction to the subject, but there is something about the topic that makes it likely that even the experienced developer will find out something new from reading it.… Read more
The 'bin packing' problem isn't just a fascination for computer scientists, but comes up in a whole range of real-world applications. It isn't that easy to come up with a practical, set oriented solution in SQL that gives a near-optimal result. … Read more
Voting systems can become very complex, and some of them are easy to manipulate by tactical voting. Joe takes a couple of voting systems and wonders how you would implement them in SQL. He's even more curious as to how you, the reader, would do so. … Read more
Unlike the hierarchical database model, which created a tree structure in which to store data, the network model formed a generalized 'graph' structure that describes the relationships between the nodes. Nowadays, the relational model is used to solve the problems for which the network model was created, but the old 'network' solutions are still being implemented by programmers, even when they are less effective.… Read more
The sequential nature of early data storage devices such as punched card and magnetic tape once forced programmers to devise algorithms that made the best of sequential access. These ways of doing data-processing have become so entrenched that they are still used in modern relational database systems. There is now a better way, as Joe explains.… Read more
It is certainly possible to fake an Array in SQL, but there are only a few occasions when it would be the best design. Most often, the wish for an array in SQL is a sign of a forlorn struggle against poorly-normalised data. One of the worst sins against Codd is the repeating group, as Joe explains.… Read more
Identifiers aren't locators, and they aren't pointers or links either. They are a logical concept in a relational database, and, unlike the more traditional methods of accessing data, don't derive from the way that data gets stored. Identifiers uniquely identify members of the set, and it should be possible to validate and verify them. Celko somehow involves watches and taxi cabs to illustrate the point.
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If you are still using the old Sybase DateTime datatype, it is a good idea to move your code to the more standard datatypes that were introduced in SQL Server 2008. Joe Celko explains why, and walks through some of the history of the TSQL way of storing and manipulating dates and times.
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The most persistent struggle in data processing has been to ensure clean data. There are many ways that data can be incorrect and a database must check, as best it can, that the data is correct. The CHECK constraint is ideally suited for this sort of work, and the checking routine can become quite complex when dealing with check digits in data.
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It is dangerous to assume that your data is sound. SQL already has intrinsic ways to cope with missing, or unknown data in its comparison predicate operators, or Theta operators. Can SQL be more effective in the way it deals with data quality? Joe Celko describes how the SQL Standard could soon evolve to deal with data in ways that allow aggregation and windowing in cases where the data quality is less than perfect
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Lookup tables can be a force for good in a relational database. Whereas the 'One True Lookup Table' remains a classic of bad database design, an auxiliary table that holds static data, and is used to lookup values, still has powerful magic. Joe Celko explains....
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The BIT data type is an awkward fit for a SQL database. It doesn't have just two values, and it can do unexpected things in expressions. What is worse, it is a flag rather than a predicate, and so its overuse, along with bit masks, is a prime candidate for being listed as a 'SQL Code Smell'. Joe Celko makes the case.
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