how to sort rows according to multiple dependencies - postgresql

Question

The table has many columns, but for the problematic part let's assume only two, [ID] and [dependency].
[Dependency] means which [ID]s should be listed before this [ID].
Each row has its unique [ID] but it might have none, one or more dependencies in the [Dependency] column
ID
Dependency
1
4
2
null
3
1,2
4
2
5
1,2,4
Expected Result
ID
Dependency
2
null
4
2
1
4
3
1,2
5
1,2,4
I have no prior experience in Postgres, I found this very useful:
SELECT aa.dep_id::integer FROM unnest(string_to_array(ss.dependency, ',')) aa(dep_id)
But still, I can't make it right.
EDIT: Added one row with 3 dependencies'
http://sqlfiddle.com/#!15/894c3/4

Answer 1

Use a recursive CTE:
WITH RECURSIVE o AS (
SELECT ss.id, ss.dependency,
1 AS level
FROM ss
WHERE dependency IS NULL
UNION ALL
SELECT ss.id, ss.dependency,
o.level + 1
FROM ss
JOIN o
ON o.id IN (SELECT x
FROM unnest(ss.dependency) AS x(x)
)
)
SELECT o.id, o.dependency
FROM o
GROUP BY o.id, o.dependency
ORDER BY max(o.level);

Answer 2

My working solution, I hope it can be improved
DO $do$
DECLARE v_RowCountInt Int;
--copy all values to temp table
begin
--This is the origin table, all rows to sort
drop table if exists _tempAll;
create temp table _tempAll as select id, dependency from XXXXX;
-- create temp table for results
drop table if exists _tempSort;
create temp table _tempSort (
id integer
,dependency varchar
,pos serial primary key);
-- move all IDs with no depencencies
WITH tmp AS (DELETE FROM _tempAll where dependency is null RETURNING id, dependency)
INSERT INTO _tempSort ( id, dependency)
SELECT id, dependency FROM tmp;
GET DIAGNOSTICS v_RowCountInt = ROW_COUNT;
while v_RowCountInt>0 loop
-- move rows with all dependencies met
WITH tmp AS (DELETE FROM _tempAll a
where a.id in(SELECT a.id FROM _tempSort s inner join _tempAll a on
s.id in (select split.dep_sid::integer from unnest(string_to_array(a.dependency, ',')) split(dep_sid))
group by a.id, a.dependency
-- verify all dependencies are already sorted
having count(*)=(CHAR_LENGTH(a.dependency) - CHAR_LENGTH(REPLACE(a.dependency, ',', ''))+1))
RETURNING a.id, a.dependency)
INSERT INTO _tempSort (id, dependency)
SELECT id, dependency FROM tmp;
GET DIAGNOSTICS v_RowCountInt = ROW_COUNT;
end loop;
end;
$do$