Why does a missing join condition create duplicate or huge results?

SQL joins · Freshers and experienced

Model answer

Without a correct ON condition each row matches many rows, giving a Cartesian product. Duplicates can also come from one-to-many relationships: joining customers to orders repeats customer data per order. Check row counts after joins, and aggregate carefully.

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SQL JOINs: INNER JOIN and LEFT JOIN Explained in the course SQL for Beginners: Learn Databases Step by Step.

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