解：（1）SELECT SNO,SNAME,STATUS
FROM S
WHERE CITY=’北京’
（2）SELECT JNO
FROM SPJ
WHERE SNO=’S2’
（3）方法一：
SELECT PNAME,WEIGHT
FROM SPJ,P
WHERE SPJ.PNO=P.PNO AND SPJ.SNO=’S6’
方法二：
SELECT PNAME,WEIGHT
FROM P
WHERE PNO IN
(SELECT PNO
FROM SPJ
WHERE SPJ.SNO=’S6’)
方法三：
SELECT PNAME,WEIGHT
FROM P
WHERE EXISTS
(SELECT *
FROM SPJ
WHERE SPJ.PNO=P.PNO AND SPJ.SNO=’S6’)
注：能够省略所属表前缀省略也对
（4） SELECT PNAME,COLOR,QTY
FROM SPJ,P
WHERE SPJ.PNO=P.PNO AND SPJ.JNO=’J1’