How do we know that the SQL query will return the correct solution?

SQL and I are just "getting to know each other" with the help of some courses and a textbook. Please help me with the theoretical and naive question of how does one know that a query returns the correct and presumably the one and only correct solution? This is clearly verifiable in the case of practice problems and although I don't get it right the first time, this is exactly what makes me think that in the real world I …

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