How to execute queries with data output with comparison conditions inside a table in PostgreSQL?

Question

PostgreSQL

Here is a table with the following content:

id	name	parent_id
one	Test 01	0
2	Test 02	0
3	Test 03	0
4	Sub test 01	one
5	Sub test 02	one
6	Sub test 03	one

As you can see from the example, records with ID 4-6 are child items of record with ID 1.
So I can’t figure out how to build a query so that as a result of issuing I have the following table:

id	name	parent_id	parent
one	Test 01	0	NULL
2	Test 02	0	NULL
3	Test 03	0	NULL
4	Sub test 01	one	Test 01
5	Sub test 02	one	Test 01
6	Sub test 03	one	Test 01

Answer 1

Select tbl1.*, tbl2.name as parent
From mytable as tbl1
Left outer join mytable as tbl2 on tbl1.parent=tbl2.id