Sql 甲骨文顶点树三层以上

我有以下sql代码来生成APEX中的树：

select 1 as status, 1 pid, 'Fehlermeldungen' as titel, null as icon, '1' as value, NULL as tooltip, NULL as link from dual
union
select -1 as status, 2 pid, k.kname as titel, NULL as icon, k.knr||'0' as value, NULL as tooltip, NULL as link from kunde k where 
(select count(fmtext) from fehlermeldung f where f.knr = k.knr) > 0
union
select 0 as status, 3 pid, fmtext as titel, NULL as icon, k.knr||fmnr as value, NULL as tooltip, null as link from kunde k, fehlermeldung f where f.knr = k.knr
order by value

现在，我想添加第四层，但如果我尝试使用pid=4创建另一个并集，则该条目将附加到最后一个select。

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我该如何处理这个问题呢？

首先，我试着重新格式化您的代码。看来你所描述的应该很好用。我想你试过这样的方法：

select 1 as status, 1 pid, 'Fehlermeldungen' as titel, null as icon, '1' as value, 
       NULL as tooltip, NULL as link from dual
union
select -1 as status, 2 pid, k.kname as titel, NULL as icon, k.knr||'0' as value, 
       NULL as tooltip, NULL as link from kunde k 
where (select count(fmtext) from fehlermeldung f where f.knr = k.knr) > 0
union
select 0 as status, 3 pid, fmtext as titel, NULL as icon, k.knr||fmnr as value, 
       NULL as tooltip, null as link from kunde k, fehlermeldung f 
where f.knr = k.knr
-- begin my new lines...
union
select 0 as status, 4 pid, 'blank' as titel, NULL as icon, '4' as value, 
       NULL as tooltip, null as link from dual 
-- end my new lines...
order by 5

是否可能将附加选择插入错误的位置？向我们展示您所做的工作，这样就更容易进行故障排除