MySql order multiple columns consider multiple - mysql

Question

id | p_id
--------------------------
1 | 0
2 | 0
3 | 1
4 | 2
5 | 0
6 | 7
7 | 1
8 | 0
This is above table data's, if i give
SELECT * from tablename order by `id` asc
it will bring the above result set
But my use case is i need to sort by both the id and p_id in a different way (i.e) i need to get result set by like below
id | p_id
--------------------------
1 | 0
3 | 1
7 | 1
6 | 7
2 | 0
4 | 2
5 | 0
8 | 0
let me explain briefly about that, p_id value 1 should be the next to the id 1 and that is arranged like above, it clearly show that p_id 1 and p_id 2 is next to the id 1 and 2 respectively and make sure that id 7 in order and id 6 next to id 7

Answer 1

If I understood you correctly , you want the order to be -> If P_id=0 then to order by ID , else, order by p_id.
You can achieve this by conditional ordering using CASE EXPRESSION :
SELECT *
FROM YourTable t
ORDER BY CASE WHEN t.pid = 0
THEN t.id
ELSE t.p_id
END ASC,
t.id
This should return you your expected results.

Answer 2

You need to know the relationship between the id's and since the 2 id blocks have different sort requirements you also need a helper column and a subquery.
create table t (id int, pid int)
insert into t
values
( 1 , 0),
( 2 , 0),
( 3 , 1),
( 4 , 2),
( 5 , 0),
( 6 , 7),
( 7 , 1),
( 8 , 0)
select s.id,s.pid
from
(
select case
when t.id in (1,3,7,6) then 1
else 2
end as ac
,
case
when t.id in (1,3,7,6) then pid
else id
end as sortcol
,
t.*
from t
) s
order by s.ac,s.sortcol
Result
id pid
1 0
3 1
7 1
6 7
2 0
4 2
5 0
8 0