如何制作一个sql循环? [英] how to make a sql loop?

问题描述

这是简化表

filesystem (id, name, parentId);

和一些条目

(1, 'root', NULL)
(2, 'folder', 1)
(3, 'subfolder', 2)
(4, 'subsubfolder', 3)

有没有办法使用原生 SQL 打印一个条目的绝对路径?

is there a way using native SQL to print the absolute path of one entry ?

例如，最后一个条目将打印root/folder/subfolder/subsubfolder".条目 2 将打印根/文件夹"等.

for instance, the last entry would print 'root/folder/subfolder/subsubfolder'. the entry 2 would print 'root/folder' and so on.

推荐答案

您没有说明您的 DBMS，以下是标准 (ANSI) SQL:

You didn't state your DBMS, the following is standard (ANSI) SQL:

with recursive folder_tree as (
   select id, name, parentid, name as fullpath
   from filesystem
   where parentid is null
   union all 
   select c.id, c.name, c.parentid, p.fullpath||'/'||c.name 
   from filesystem c
      join folder_tree p on c.parentid = p.id
)
select *
from folder_tree

SQLFiddle:http://sqlfiddle.com/#!15/91332/7

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