仅保留第一列的第一个值并根据层次结构对其他两列进行排序

Question

所以有五个人在 Laugh 工厂工作。 Marc 先上来，然后是 Judy，然后是 Lorie，然后是 Agnes，最后是 Isaiah。

我想从这里开始：

+------------------------------+
| Laugh Factory |Marc | Judy   |
| Laugh Factory |Judy | Lorie  |
| Laugh Factory |Lorie| Agnes  |
| Laugh Factory |Agnes| Isaiah |
+------------------------------+

为此：

 Laugh Factory | Marc | Judy | Lorie | Agnes | Isaiah

我该如何实现？

Answer 1

为此你需要 recursive query。

沿线的东西（未经测试）：

with recursive tree as (
  select company, comedian, preceding_comedian, 1 as level
  from the_table
  where company = 'Laugh Factory'
    and preceding_comedian is null
  union all
  select ch.company, ch.comedian, ch.preceding_comedian, p.level + 1
  from the_table ch
    join tree p on ch.preceding_comedian = p.comedian
)
select company, string_agg(comedian, ' > ' order by level) as comedians
from tree 
group by company;