在自引用表上获得第 n 级

Question

我有一个最多有 5 个级别的自引用表

groupid   | parentid  | detail
--------- | --------- | ---------
Group A   | Highest   | nope 
Group B   | Group A   | i need this  
Highest   | NULL      | nope 
Group C   | Group B   | nope 
Group D   | Group C   | nope 

我有一个事务表，它在上面的表中查找 groupid 以检索其中 groupid = Group B 的详细值。事务表上 groupid 的值仅在 Group B 到 D 之间，并且永远不会更高.

txnid     | groupid   | desired   | desired
--------- | --------- | --------- | ---------
1         | Group D   | Group B   | i need this
2         | Group B   | Group B   | i need this
3         | Group C   | Group B   | i need this
4         | Group B   | Group B   | i need this

我的 T-SQL 脚本应该如何获得所需的列？我可以多次离开加入到自引用表中，直到 B 组我需要重新加入的时间不一致。

非常感谢任何想法！

Answer 1

我仍然不清楚你怎么知道哪个是 GROUP B，我想这是它的父级为空的记录。

create table org(groupid char(1), parentid char(1), details varchar(20));
insert into org values
('a', null, 'nope'),('b', 'a', 'I need this'),('c', 'b', 'nope'),('d', 'c', 'nope'),('e', 'd', 'nope');

create table trans(id int, groupid char(1));
insert into trans values
(1, 'b'),(2, 'c'),(3, 'c'),(4, 'd'),(5, 'e');
GO

10 行受影响

with all_levels as
(
    select     ob.groupid groupid_b, oc.groupid groupid_c, 
               od.groupid groupid_d, oe.groupid groupid_e, 
               ob.details
    from       org ob
    inner join org oc
    on         oc.parentid = ob.groupid
    inner join org od
    on         od.parentid = oc.groupid
    inner join org oe
    on         oe.parentid = od.groupid
    where      ob.parentid is not null
) select * from all_levels;

GO

groupid_b | groupid_c | groupid_d | groupid_e |细节 :-------- | :-------- | :-------- | :-------- | :---------- 乙 | c | d |电子|我需要这个

--= build a 4 levels row
with all_levels as
(
    select     ob.groupid groupid_b, oc.groupid groupid_c, 
               od.groupid groupid_d, oe.groupid groupid_e, 
               ob.details
    from       org ob
    inner join org oc
    on         oc.parentid = ob.groupid
    inner join org od
    on         od.parentid = oc.groupid
    inner join org oe
    on         oe.parentid = od.groupid
    where      ob.parentid is not null
) 
    --= no matter what groupid returns b group details
    , only_b as
    (
        select groupid_b as groupid, groupid_b, details from all_levels
        union all
        select groupid_c as groupid, groupid_b, details from all_levels
        union all
        select groupid_d as groupid, groupid_b, details from all_levels
        union all
        select groupid_e as groupid, groupid_b, details from all_levels
    )
    --= join with transactions table
    select     id, t.groupid, groupid_b, ob.details
    from       trans t
    inner join only_b ob
    on         ob.groupid = t.groupid;
GO

编号 |组ID | groupid_b |细节 -: | :-------- | :-------- | :---------- 1 |乙 |乙 |我需要这个 2 | c |乙 |我需要这个 3 | c |乙 |我需要这个 4 | d |乙 |我需要这个 5 |电子|乙 |我需要这个

dbfiddle here

您也可以处理递归函数，但我认为它在性能方面不会更好。

create function findDetails(@groupid char(1))
returns varchar(100)
as
begin
    declare @parentid char(1) = '1';
    declare @next_parentid char(1) = '1';
    declare @details varchar(100) = '';

    while @next_parentid is not null
    begin
        select     @details = org.details, @parentid = org.parentid, @next_parentid = op.parentid
        from       org
        inner join org op
        on         op.groupid = org.parentid
        where      org.groupid = @groupid

        set @groupid = @parentid;
    end

    return @details;
end
GO

✓

select id, groupid, dbo.findDetails(groupid) as details_b
from   trans;
GO

编号 |组ID |细节_b -: | :-------- | :---------- 1 |乙 |我需要这个 2 | c |我需要这个 3 | c |我需要这个 4 | d |我需要这个 5 |电子|我需要这个

dbfiddle here