@ Symbol - a solution for Recursive SELECT query in Mysql?

Question

there are a lot of questions about Recursive SELECT query in Mysql, but most of answers is that \"There NO solution for Recursive SELECT query in Mysql\".

Actually t

Answer 1

In my limited deep of hierarchy-levels, I used the following:

parents:

select * from mytable
join (
    select A.id Aid,B.id Bid, C.id Cid, D.id Did, E.id Eid, F.id Fid,G.id Gid, H.id Hid from mytable A
    left join mytable B on B.id=A.parent
    left join mytable C on C.id=B.parent
    left join mytable D on D.id=C.parent
    left join mytable E on E.id=D.parent
    left join mytable F on F.id=E.parent
    left join mytable G on G.id=F.parent
    left join mytable H on H.id=G.parent
    where A.id=9
) X
where id in (Aid,Bid,Cid,Did,Eid,Fid,Gid,Hid);

children:

select * from mytable where id in (
select distinct id from mytable
join (
    select A.id Aid,B.id Bid, C.id Cid, D.id Did, E.id Eid, F.id Fid,G.id Gid, H.id Hid FROM mytable A
    left join mytable B on B.parent=A.id
    left join mytable C on C.parent=B.id
    left join mytable D on D.parent=C.id
    left join mytable E on E.parent=D.id
    left join mytable F on F.parent=E.id
    left join mytable G on G.parent=F.id
    left join mytable H on H.parent=G.id
    Where A.id=1
) X
where id in (Aid,Bid,Cid,Did,Eid,Fid,Gid,Hid)

);

Answer 2

I keep wondering if something like this would work:

select distinct col1, col2
from (select col1, col2,
             @pv:=(case when find_in_set(col3, @pv) then @pv else concat(@pv, ',', col3) 
                   end) as 'col3'
      from table1 join
          (select @pv:='1') tmp
          on find_in_set(col1, @pv) > 0
     ) t

Something like this should work for small data sets. However, the idea of putting all the ids in a string is limited to the capacity of a string.

Answer 3

Stored procedure is the best way to do it. Because Gordon's solution would work only if the data follows the same order.

If we have a table structure like this

col1 - col2 - col3
3 - k - 7
5 - d - 3
1 - a - 5
6 - o - 2
2 - 0 - 8

It wont work.

Here is a sample procedure code to achieve the same.

delimiter //
CREATE PROCEDURE chainReaction 
(
    in inputNo int
) 
BEGIN 
    declare final_id int default NULL;
    SELECT col3 into final_id from table1
    where col1 = inputNo;
    if( final_id is not null) then
        insert into results(select col1, col2, col3 from table1 where col1 = inputNo);
        CALL chainReaction(final_id);   
    end if;
END//
delimiter ;

call chainReaction(1);
select * from results;
drop table if exists results;

Answer 4

Had more of a play. Can't get it to work using the user variables due to the ordering of items.

However if you have a reasonable maximum number of levels then you can do something like this:-

SELECT CONCAT_WS('-', a.allCols, b.allCols, c.allCols, d.allCols, e.allCols, f.allCols, g.allCols, h.allCols, i.allCols, j.allCols, k.allCols, l.allCols, m.allCols)
FROM (SELECT col1, col3, CONCAT(col1, col2, col3) AS allCols FROM table1) a
LEFT OUTER JOIN(SELECT col1, col3, CONCAT(col1, col2, col3) AS allCols FROM table1) b ON a.col3 = b.col1
LEFT OUTER JOIN(SELECT col1, col3, CONCAT(col1, col2, col3) AS allCols FROM table1) c ON b.col3 = c.col1
LEFT OUTER JOIN(SELECT col1, col3, CONCAT(col1, col2, col3) AS allCols FROM table1) d ON c.col3 = d.col1
LEFT OUTER JOIN(SELECT col1, col3, CONCAT(col1, col2, col3) AS allCols FROM table1) e ON d.col3 = e.col1
LEFT OUTER JOIN(SELECT col1, col3, CONCAT(col1, col2, col3) AS allCols FROM table1) f ON e.col3 = f.col1
LEFT OUTER JOIN(SELECT col1, col3, CONCAT(col1, col2, col3) AS allCols FROM table1) g ON f.col3 = g.col1
LEFT OUTER JOIN(SELECT col1, col3, CONCAT(col1, col2, col3) AS allCols FROM table1) h ON g.col3 = h.col1
LEFT OUTER JOIN(SELECT col1, col3, CONCAT(col1, col2, col3) AS allCols FROM table1) i ON h.col3 = i.col1
LEFT OUTER JOIN(SELECT col1, col3, CONCAT(col1, col2, col3) AS allCols FROM table1) j ON i.col3 = j.col1
LEFT OUTER JOIN(SELECT col1, col3, CONCAT(col1, col2, col3) AS allCols FROM table1) k ON j.col3 = k.col1
LEFT OUTER JOIN(SELECT col1, col3, CONCAT(col1, col2, col3) AS allCols FROM table1) l ON k.col3 = l.col1
LEFT OUTER JOIN(SELECT col1, col3, CONCAT(col1, col2, col3) AS allCols FROM table1) m ON l.col3 = m.col1
WHERE a.col1 = 1

This is coping with up to 13 levels (OK, only a couple used in your test data), and will give a comma separated bit for each column, with each row joined with a dash (-).