编辑代码

(1) SELECT JNO 
    FROM J
    WHERE CITY = '北京';

(2) SELECT DISTINCT S.SNO,SNAME
    FROM SPJ,S
    WHERE PNO  IN(
        SELECT DISTINCT PNO
        FROM P
        WHERE COLOR = '红'
    ) AND S.SNO = SPJ.SNO;

(3) SELECT DISTINCT S.SNO,SNAME
    FROM SPJ,S
    WHERE PNO NOT IN(
        SELECT DISTINCT PNO
        FROM P
        WHERE COLOR = '红'
    ) AND S.SNO = SPJ.SNO;

(4) SELECT DISTINCT S.SNO,SNAME
    FROM S
    WHERE NOT EXISTS(
        SELECT PNO
				FROM P
				WHERE NOT EXISTS(
					SELECT SPJ.PNO
						FROM SPJ
						WHERE S.SNO = SPJ.PNO
						AND P.PNO = SPJ.PNO
				) 
    );

(5) SELECT DISTINCT S.SNO,SNAME
    FROM S
    WHERE S.SNO IN(
        SELECT SPJ.SNO
				FROM SPJ
				GROUP BY SNO
				HAVING COUNT(*)=(
					SELECT COUNT(*)
						FROM J
				)
); 

(6) SELECT SNO,SNAME
    FROM s
    WHERE S.SNO  IN (
	    SELECT SNO
	    FROM spj
	    WHERE JNO =(
		    SELECT JNO
		    FROM j
		    WHERE CITY = '北京'
	    )
	    GROUP BY SNO
	    HAVING COUNT(*) = (
		    SELECT COUNT(*)
		    FROM p
	    )
    );