两个关系模式R = (A, B, C, D) 和 S = (B, C, D), 用他们创建了两个关系r(R) and s(S)
答案:1 悬赏:60
解决时间 2021-01-30 00:48
- 提问者网友:爱了却不能说
- 2021-01-29 08:11
两个关系模式R = (A, B, C, D) 和 S = (B, C, D), 用他们创建了两个关系r(R) and s(S)
最佳答案
- 二级知识专家网友:人间朝暮
- 2021-01-29 08:57
第一种方法:select A from r T1 where not exists(
select B,C,D from s where not exists(
select A from r T2 where T2.B=s.B and T2.C=s.C and T2.D=s.D and T1.A=T2.A))
第二种方法:
SELECt DISTINCT A
FROM r a
WHERe NOT EXISTS
(SELECt * FROM
(SELECt B,C,D FROM r b
WHERe a.A = b.A) x
RIGHT OUTER JOIN
(SELECt B,C,D FROM s) y
ON x.B = y.B and x.C=y.C and x.D=y.D
WHERe (x.B IS NULL and x.C is null and x.D is null))
你试一下行不行,不行的话,但基本上就是这个思路,可以自己改一改。
select B,C,D from s where not exists(
select A from r T2 where T2.B=s.B and T2.C=s.C and T2.D=s.D and T1.A=T2.A))
第二种方法:
SELECt DISTINCT A
FROM r a
WHERe NOT EXISTS
(SELECt * FROM
(SELECt B,C,D FROM r b
WHERe a.A = b.A) x
RIGHT OUTER JOIN
(SELECt B,C,D FROM s) y
ON x.B = y.B and x.C=y.C and x.D=y.D
WHERe (x.B IS NULL and x.C is null and x.D is null))
你试一下行不行,不行的话,但基本上就是这个思路,可以自己改一改。
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