Cartesian product in SQL is a term from the set theory of mathematics. However, we can also find this term in SQL database manuals. What does it mean, and how should we work with it? Let’s learn it.

A Cartesian product of two sets X and Y, denoted X × Y, is the set of all ordered pairs where x is in X and y is in Y.

In terms of SQL, the Cartesian product is a new table formed of two tables. If those tables have 3 and 4 lines respectively, the Cartesian product table will have 3×4 lines. Therefore, each row from the first table joins each row of the second table. You get the multiplication result of two sets making all possible ordered pairs of the original sets’ elements.

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