Question

我有几张桌子。一个包含组的表：

[ID] - [ParentGroupID]
1    - NULL
2      1
3      1
4      2

另一个有设置

[Setting] - [GroupId] - [Value]
Title       1           Hello
Title       2           World

如果我查询第3组的标题，我现在想要“你好” 如果我查询第4组的标题（而不是“Hello”），我想回到“世界”

有没有办法在MSSQL中有效地执行此操作？目前我正在代码中递归地解决这个问题。但是我希望SQL可以为我解决这个问题。

Answer 1

不知道SQL Server语法，但是如下所示？

SELECT settings.value FROM settings JOIN groups ON settings.groupid = groups.parentgroupid WHERE settings.setting = 'Title' AND groups.id = 3

Answer 2

这是我们公司多次遇到的问题。这适用于任何情况，包括何时只能在某些级别而不是其他级别设置设置（请参阅SQL小提琴http://sqlfiddle.com/#!3/16af0/1/0：

With GroupSettings(group_id, parent_group_id, value, current_level)
As
(
    Select g.id as group_id, g.parent_id, s.value, 0 As current_Level
    From Groups As g
    Join Settings As s On s.group_id = g.id
    Where g.parent_id Is Null
    Union All
    Select g.id, g.parent_id, Coalesce((Select value From Settings s Where s.group_id=g.id), gs.value), current_level+1
    From GroupSettings as gs
    Join Groups As g On g.parent_id = gs.group_id
)

Select *
From GroupSettings
Where group_id=4

Answer 3

我相信以下是您所寻求的。请参阅sqlfiddle

SELECT vALUE FROM
Groups g inner join Settings s 
ON g.ParentGroupId = s.GroupID
WHERE g.ID = 3 -- will return Hello,], set ID = 4 will return World

如何使用分层设置结构中的值获得第一个条目？

3 个答案: