Historically, in order to explain the concept of JOIN clause authors of textbooks and tutorials use a Venn diagram. I do not know who was the first to use it, but this addiction firmly stuck in the minds of everyone who has ever explained an operator of the connection in SQL. I will show flaws of this approach by giving you an example.

Using SQL every day for many years, I have found for myself a few useful tricks. Maybe it cannot be called full-fledged tricks, but rather approaches to solving certain simple tasks that save us time and effort.

Sometimes enough a few effective tricks to get promoted. Learn how you can work more efficiently in Excel using five simple tricks.

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It would be wrong to say that all flow control in SQL ends at CASE WHEN in SELECT clause (Control flow in SQL). This method of using has a greater effect on the "visual" component of the result, leaving aside the business logic and optimisation mechanisms. I can describe at least two more ways of using CASE WHEN clause: within the HAVING/WHERE clause and within the JOIN clause.