Date R( A , B, C) e S( A , B, C) quali delle seguenti interrogazioni sono equivalenti?

Question

Date R( A , B, C) e S( A , B, C) quali delle seguenti interrogazioni sono equivalenti?

Accepted Answer

SELECT * FROM R  WHERE EXISTS (SELECT * FROM S WHERE R.A=S.A AND R.B=S.B AND R.C=S.C)

Accepted Answer

SELECT *   FROM R  WHERE (A, B, C) IN (SELECT * FROM S)

Answer

SELECT *  FROM R WHERE A IN (SELECT * FROM S)

Answer

SELECT *  FROM R INTERSECT SELECT *  FROM S

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