Joins are the heart of SQL, and the real signal is precise semantics: semi/anti joins (EXISTS / NOT EXISTS), the NOT IN null trap, and the fan-out bug that silently doubles your sums.
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Explain SQL join types (inner, left/right/full outer, semi, anti, cross) and when to use each.
Joins are the heart of SQL, and the real signal is precise semantics: semi/anti joins (EXISTS / NOT EXISTS), the NOT IN null trap, and the fan-out bug that silently doubles your sums.
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