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Data & Analytics · Intermediate

CROSS JOIN

A join with no condition that returns every combination of rows from both tables (the Cartesian product).

Definition

If table A has m rows and B has n rows, a CROSS JOIN returns m × n rows. It is intentionally used to generate combinations such as every store × every date, but an accidental Cartesian product from a missing join condition can explode row counts.

Example

SELECT s.StoreID, d.Date FROM Stores s CROSS JOIN Calendar d;

Exam tip

A huge, unexpected row count usually means a missing or incorrect join predicate (an accidental Cartesian product).

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