Postgresql递归自联接

我在postgres中的表如下所示,表存储了ID之间的一种链式关系,我想要一个可以产生结果的查询,如“vc1” – > “rc7”或“vc3” – >“rc7”,我只会查询第一列ID1中的ID

ID1     ID2
"vc1"   "vc2"
"vc2"   "vc3"
"vc3"   "vc4"
"vc4"   "rc7"

所以我想在这里提供一些“头”ID,我必须获取尾部(链中的最后一个)id.

这是使用递归CTE的sql：

with recursive tr(id1,id2,level) as (
      select t.id1,t.id2,1 as level
      from t union all
      select t.id1,tr.id2,tr.level + 1
      from t join
           tr
           on t.id2 = tr.id1
     )
select *
from (select tr.*,max(level) over (partition by id1) as maxlevel
      from tr
     ) tr
where level = maxlevel;

Here是sqlfiddle

原文地址：https://www.jb51.cc/postgresql/191885.html