我有这张桌子(Prefrences_Table)
--------------------------
|student | Preferences |
--------------------------
Stud A | Stud B
Stud A | Stud C
Stud B | Stud E
Stud B | Stud A
Stud C | Stud F
Stud F | Stud B
--------------------------
如果“Stud A”在他的首选项列表中添加了“Stud B”,我想检查“stud B”是否在他的偏好中添加了“stud A”,所以我可以将它们添加到一个组中。 如何使用SQL或C#完成此操作?
答案 0 :(得分:4)
自我加入应该在这里工作得很好。附加谓词仅返回匹配的第一个实例以避免重复。
select t.student, t1.student
from
Prefrences_Table t
inner join Prefrences_Table t1
on t.student = t1.preferences
and t.preferences = t1.student
and t.student < t1.student
答案 1 :(得分:3)
这可能会让你回答你的问题,如果两个学生在偏好中添加了另一个,则字段互为,否则为零
SELECT T1.student, T2.Preferences,
(SELECT COUNT(*) FROM Prefrences_Table T2 WHERE T2.Preferences = T1.student AND T2.student = T1.Preferences) AS mutual
FROM Prefrences_Table T1
答案 2 :(得分:1)
另一种选择是:
SELECT * FROM
(
SELECT PM.student, PM.Preferences,
(SELECT COUNT(student) FROM Prefrences_Table AS PI WHERE PI.Preferences = PM.student
AND PI.student = PM.Preferences) AS CheckCross
FROM Prefrences_Table AS PM
) AS PD
WHERE PD.CheckCross > 0
答案 3 :(得分:1)
你有一些SQL答案,这里是c#/ linq中的一个。
var list = new List<Prefrences_Table>();
var results = (from t in list
join t1 in list on t.student equals t1.preferences
where
t.student == t1.preferences &&
t.preferences == t1.student &&
string.CompareOrdinal(t.student, t1.student) < 0
select new {t.student, t1.student}
);
答案 4 :(得分:1)
您可以使用:
CREATE PROCEDURE dbo.CheckGroup
(
@pStudent1 INT,
@pStudent2 INT
)
BEGIN
IF EXISTS
(
SELECT *
FROM Prefrences_Table t
WHERE t.Student = @pStudent1 AND t.Preferences = @pStudent2
) AND EXISTS
(
SELECT *
FROM Prefrences_Table t
WHERE t.Student = @pStudent2 AND t.Preferences = @pStudent1
)
BEGIN
... do something
END
ELSE
BEGIN
... do somethingelse
END
END