Missing Data
When we don't have all the information needed to model data, we often use NULL. However, that causes other issues.
2021-04-12
2,767 reads
Joe Celko
Mathematicians and SQL
Georg Ferdinand Ludwig Philipp Cantor is considered the creator of set theory, and his theories are the basis for the naïve set theory you learned in school. But there are lots of other mathematicians you should know, such as Hilbert, Frege, Russell, Zermelo and Dedekind. They made a lot of contributions, too. Hilbert Hilbert is […]
2021-01-19
5,622 reads
Data Element Names and Scoping Rules in SQL
How you name data elements in databases and applications programs has often been a matter of personal taste. Decades ago, when I worked for state government, there is a COBOL programmer who would pick a theme for his programs. The paragraphs and variables would be named based on the current theme. One of his programs […]
2021-01-11
2,170 reads
2020-10-12
1,993 reads
Arrays in SQL that Avoid Repeated Groups
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 Celko explains.
2011-07-20
3,438 reads
Improving Comparison Operators and Window Functions
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.
2011-04-01
6,632 reads
The DIS-Information Principle: A Splitting Headache
You can easily re-factor bad DML code, but if a database design is wrong, you can do little to rescue the problem, even with expert queries. So what constitutes 'wrong RDBMS design? What are these errors that continually crop up? How can you recognise them and fix them? Joe embarks on a new series of articles by identifying a series of bad practices based on the habit of 'splitting' that which shouldn't be split.
2010-09-08
2,767 reads
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!
2010-01-25
1,692 reads
Celko's SQL Stumper: The Data Warehouse Problem
Joe Celko comes back with a puzzle that isn't new, but one where the answer he originally gave now seems archaic: It is a deceptively simple problem, but is it true that the new features of SQL have simplified the solution? We leave it to the readers to provide the answer!
2009-09-28
3,525 reads
Celko's Summer SQL Stumpers: Prime numbers
Our first Stumper sees Joe Celko providing a conundrum with a prize for anyone who can come up with a better solution than he can.
2009-07-27
3,216 reads
Blogs
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Leadership in Times of Change: Guiding Teams Through Uncertainty, Disruption, and Transformation
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The End of Year Vacation Burn
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It’s been a good year for me. With my sabbatical, I felt like I’ve...
Forums
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how to write this query?
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Powershell script to generate SQL server Inventory in CSV format
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Question of the Day
Azure SQL Database MAXDOP
When Azure SQL Database was originally released, the MAXDOP was set to 0 for each new database. In Oct 2025, what is the default value for Azure SQL databases?
See possible answers