Question

有两个关系S(A,B,C,D)和(C,D,E,F),写出与下列查询等价的SQL表达式

第三题

Answer 1

1、σA=10（S)

select * from s where A=10
2、πA,B（S）

select A,B from S
3、πC,D（S）*T

select * from S,T where T.C=S.C and T.D=S.D
只知道三个，不好意思

Answer 2

解:
(1)select * from S where A='10';
(2)select A,B from S;
(3) select A,B,S.C,S.D,E,F from S,T where S.C=T.C and S.D=T.D;
(4)select * from S,T where S.C=T.C;
(5) select * from S,T where S.A<T.E;
(6) select S.C,S.D,T.* from S,T ;

Answer 3

1. SELECT*FROM S   WHERE A=10

2. SELECT A,B FROM S

3. SELECT A,B,S.C,S.D,E,F FROM S,T     WHERE S.C=T.C AND S.D=T.D

4. SELECT S.*,T.* FROM S,T    WHERE S.C=T.C

5. SELECT S.*,T.* FROM S,T  WHERE A<E

6. SELECT S.C,S.D,T.* FROM S,T
   

Answer 4

(4)select*
from s,t
where s.c=t.c
(5)select*
from s,t
where s.a＜t.e
(6)select s.c,s.d,t*
from s,t