设有关系R(A,B,C)和S(B,C,D),下列各关系代数表达式成立的是()
A.
B.
C.
D.
- · 有3位网友选择 D,占比33.33%
- · 有2位网友选择 B,占比22.22%
- · 有2位网友选择 C,占比22.22%
- · 有2位网友选择 A,占比22.22%
A.
B.
C.
D.
设有关系R(A,B,C)和S(C,D),与关系代数表达式等价的SQL语句是哪个?
A、select * from R,S where R.C=S.C
B、select A,B,D from R,S where R.C=S.C
C、select A,B,D from R,S where R=S
D、select A,B from R where(select D from S where R.C=S.C)
A.σR.C=S.C(πA,B,D(R×S))
B.πA,B,D(σR.C-S.C(R×S))
C.σR.C=S.C((πA,BR)×(πDS))
D.σR.C=S.C(πD((πA,BR)×S)
A.σR.C=S.C(πA,B,D(R×S))
B.πA,B,D(σR.C=S.C(R×S))
C.σR.C=S.C((πA,BR)×(πDS))
D.σR.C=S.C(πD(πA,BR)×S)
有关系代数表达式:与其执行结果等价的pgSQL语句为( )。
A、SELECT * FROM eeexam,examinee WHERE examinee.eeid=eeexam.eeid;
B、SELECT * FROM eeexam CROSS JOIN examinee WHERE examinee.eeid=eeexam.eeid;
C、SELECT * FROM eeexam NATURAL JOIN examinee;
D、SELECT * FROM eeexam JOIN examinee ON examinee.eeid=eeexam.eeid;
E、SELECT * FROM eeexam JOIN examinee USING(eeid);
F、SELECT * FROM eeexam CROSS JOIN examinee;
G、SELECT * FROM eeexam NATURAL JOIN examinee WHERE examinee.eeid=eeexam.eeid;
H、SELECT * FROM eeexam JOIN examinee WHERE examinee.eeid=eeexam.eeid;
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