问题 单项选择题

现在有两个关系模式:供应商S(Sno,Sname,Status,City)和供应情况SPJ(Sno,Pno,Jno, Qty)。对于查询“查询零件号Pno等于‘P3’的供应商名Sname”SQL语句 (221) 是错误的,而关系代数表达式 (222) 是正确的。

A.SELECTSname FROM S WHERE EXIST5 (SELECT * FROM SPJ WHERE S.Sno=SPJ.Sno AND SPJ.Pno=’P3’)
B.SELECT Sname FROM S,SPJ WHERE S.Sno=SPJ.Sno AND SPJ.Pno=’P3’) CROUP BY Sname
C.SELECT DISTINCT Sname FROM S WHERE EXISTS (SELECT * FROM SPJ WHERE S.Sno=SPJ.Sno AND SPJ.Pno=’P3’)
D.SELECT DISTINCT Sname FROM S WHERERE 0< (SELECTCOUNT(,) FROM SPJ WHERE S.Sno=SPJ.Sno AND SPJ.Pnn=’P3’)

答案

参考答案:A

单项选择题 A2型题
单项选择题