我有三个像这样定义的表:
[tbMember]
memberID | memberName
1 | John
2 | Peter
[tbGroup]
groupID | groupName
1 | Alpha
2 | Beta
3 | Gamma
[tbMemberGroupRelation]
memberID | groupID | memberRank (larger number is higher)
1 | 1 | 0
1 | 2 | 1
2 | 1 | 5
2 | 2 | 3
2 | 3 | 1
现在我想执行一个表连接选择,以获得包含(不同)成员的结果,每个行中排名最高的组,对于上面给出的示例,查询结果需要:
memberID | memberName | groupName | memberRank
1 | John | Beta | 1
2 | Peter | Alpha | 5
有没有办法在单个SQL中实现它,如下面的样式?
select * from tbMember m
left join tbMemberGroupRelation mg on (m.MemberID = mg.MemberID and ......)
left join tbGroup g on (mg.GroupID = g.GroupID)
如果无法用简单的查询进行编写,也会感激任何其他解决方案。
=========更新=========
表格中只允许一个最高等级
答案 0 :(得分:2)
一种解决方案是创建memberRank
的反转序列/等级,以便每个成员的最高等级始终等于1.
这是我使用子查询实现它的方式:
SELECT
m.memberID,
m.memberName,
g.groupName,
mg.memberRank
FROM
tbMember m
LEFT JOIN
(
SELECT
memberID,
groupID,
groupName,
memberRank,
RANK() OVER(PARTITION BY memberID ORDER BY memberRank DESC) AS invRank
FROM
tbMemberGroupRelation
) mg
ON (mg.memberID = m.memberID)
AND (mg.invRank = 1)
LEFT JOIN
tbGroup g
ON (g.groupID = mg.groupID);
答案 1 :(得分:1)
create table [tbGroup] (groupid int, groupname varchar(8000))
Insert [tbGroup] Values (1, 'Alpha')
Insert [tbGroup] Values (2, 'Beta')
Insert [tbGroup] Values (3, 'Gamma')
create table [tbMemberGroupRelation] (memberid int, groupid int, memberrank int)
Insert [tbMemberGroupRelation] Values (1,1,0)
Insert [tbMemberGroupRelation] Values (1,2,1)
Insert [tbMemberGroupRelation] Values (2,1,5)
Insert [tbMemberGroupRelation] Values (2,2,3)
Insert [tbMemberGroupRelation] Values (2,3,1)
;With cteMemberGroupRelation As
(
Select *, Row_Number() Over (Partition By MemberID Order By MemberRank Desc) SortOrder
From [tbMemberGroupRelation]
)
Select *
From tbMember M
Join (Select * From cteMemberGroupRelation Where SortOrder = 1) R On R.memberid = M.memberid
Join tbGroup G On G.groupid = R.groupid
答案 2 :(得分:1)
另一种方法:
SELECT
M.memberID,
M.memberName,
G.groupName,
MG.memberRank
FROM
Member M
LEFT OUTER JOIN MemberGroup MG ON MG.memberID = M.memberID
LEFT OUTER JOIN MemberGroup MG2 ON
MG2.memberID = M.memberID AND
MG2.memberRank > MG.memberRank
INNER JOIN [Group] G ON G.groupid = MG.groupid
WHERE
MG2.memberid IS NULL
由于索引等原因,在某些情况下可能会表现更好