POSTGRE如何從層級表中選擇父級名稱

Question

如何選擇具有父級ID的層級表？ 我有這樣

+-----------+------------+-------------+ 
| id  | parent_id | name  | 
+-----------+------------+-------------+ 
|1   | 0   | a   | 
+-----------+------------+-------------+ 
|2   | 1   | a1   | 
+-----------+------------+-------------+ 
|3   | 0   | b   | 
+-----------+------------+-------------+ 
|4   | 3   | b1   | 
+-----------+------------+-------------+ 
|5   | 3   | b2   | 
+-----------+------------+-------------+ 

一個表，我想表明這樣

+-----------+------------+-------------+ 
| id  | name  | parent  | 
+-----------+------------+-------------+ 
|1   | a   | NULL  | 
+-----------+------------+-------------+ 
|2   | a1   | a   | 
+-----------+------------+-------------+ 
|3   | b   | NULL  | 
+-----------+------------+-------------+ 
|4   | b1   | b   | 
+-----------+------------+-------------+ 
|5   | b2   | b   | 
+-----------+------------+-------------+ 

表是否有可能創建選擇這樣嗎？任何人都知道如何在Postgre或MySQL創建此，請給我一些建議，

Answer 1

只需使用一個left join：

select t1.id, t1.name, t2.name as parent 
from yourtable t1 
left join yourtable t2 
on t1.parent_id = t2.id 
order by t1.id 

Demo Here