I used to teach a data modeling class in our undergraduate Computer Information Systems program. In this class we developed data models for relational databases and prepared SQL code to interact with our databases. One of the topics we covered in this class was the different ways to join tables in a SQL query. The join command is a valuable command and can produce vastly different results if the join is not properly applied. As a result, it is important to have good understanding of the outcome for each type of join.
Earlier this week one of my former students sent me a link to a great webpage that uses Venn diagrams to illustrate the different forms of table joins. While textbooks sometimes include some diagrams to make this illustration the books are often incomplete.
Here is a
link to the website. This site not only includes the Venn diagrams but also associates the diagram with the corresponding SQL needed to apply the join and realize the visualized result.
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