All we need is an easy explanation of the problem, so here it is.
i want to relate child to parent from same table.
Table is built like this.
id, parentid, name
i want to have the complete path of the [name] columns without specify levels like i have in the example. I would like to have a better way to display path with kind of infinite levels of parent and child. i hope this make sense
this is what i have
SELECT case when s6.id is null and s5.id is null and s4.id is null and s3.id is null and s2.id is null then s1.name when s6.id is null and s5.id is null and s4.id is null and s3.id is null then s2.name || ' > ' || s1.name when s6.id is null and s5.id is null and s4.id is null then s3.name || ' > ' || s2.name || ' > ' || s1.name when s6.id is null and s5.id is null then s4.name || ' > ' || s3.name || ' > ' || s2.name || ' > ' || s1.name when s6.id is null then s5.name || ' > ' || s4.name || ' > ' || s3.name || ' > ' || s2.name || ' > ' || s1.name else 'n/a' end as path FROM mytable s1 LEFT JOIN mytable s2 ON s1.parentid = s2.id LEFT JOIN mytable s3 ON s2.parentid = s3.id LEFT JOIN mytable s4 ON s3.parentid = s4.id LEFT JOIN mytable s5 ON s4.parentid = s5.id LEFT JOIN mytable s6 ON s5.parentid = s6.id ;
thanks in advance
How to solve :
I know you bored from this bug, So we are here to help you! Take a deep breath and look at the explanation of your problem. We have many solutions to this problem, But we recommend you to use the first method because it is tested & true method that will 100% work for you.
What you’re looking for is a recursive query:
with recursive nodes(id, path) as ( -- selecting the parent/root (anchor) select r.id, r.name from mytable r where r.id = <choose starting root id> union all -- recursively going through child nodes (recursive member) select c.id, concat(path, '->', c.name) from mytable c join nodes as n on n.id = c.parent_id ) select * from nodes order by path;
Keep in mind that if you have self referencing members (or ones that reference each other in a circle), this will go into an infinite loop! So you have to either exclude such scenarios with a where statement or not allow any inserts/updates that would cause such a scenario.
Note: Use and implement method 1 because this method fully tested our system.
Thank you 🙂