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What is a LATERAL join (CROSS APPLY), and when do you need it?

A LATERAL join lets a FROM-clause subquery reference columns from the table before it, which a normal join cannot. The signal is recognizing the per-row use cases: top-N per group, table functions, unnesting arrays.

Updated Aug 2026 · Grounded in real Applied AI Engineer interview loops and written to a senior-engineer editorial bar.

A LATERAL join lets a FROM-clause subquery reference columns from the table before it, which a normal join cannot. The signal is recognizing the per-row use cases: top-N per group, table functions, unnesting arrays.

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