How to implement double SELECT in recursive cte on SQL? - sql

Question

I faced a problem while implementing a recursive query on SQL, including double selection from the database at each iteration.
I have two tables, describing the oriented graph, where each nodes located at grid:
table nodes:
id
grid_x
grid_y
table edges:
source
target
And want to implement selection of nodes, which located at adjacent positions on the grid to the right of the initial node with selection of parents and childs at each iteration.
Selection of right nodes realized by following recursive query:
WITH RECURSIVE
cte(id, grid_x, grid_y) AS (
SELECT id, grid_x, grid_y
FROM nodes WHERE id = 0
UNION ALL
SELECT current.id, current.grid_x, current.grid_y
FROM nodes AS current, cte AS prev
WHERE current.grid_x = prev.grid_x + 1
AND current.grid_y = prev.grid_y
)
SELECT * FROM cte;
let the data in the database have the following representation
i.e.
Table nodes:
id | grid_x | grid_y | |
----+--------+--------+---+--
0 | 0 | 0 | |
13 | 1 | 0 | |
14 | 3 | 0 | |
5 | -1 | 1 | |
1 | 0 | 1 | |
2 | 1 | 1 | |
3 | 2 | 1 | |
4 | 4 | 1 | |
12 | -2 | 2 | |
6 | -1 | 2 | |
7 | 0 | 2 | |
8 | 2 | 2 | |
9 | 3 | 2 | |
10 | 4 | 2 | |
11 | 6 | 2 | |
Table edges:
id | source | target
----+--------+--------
1 | 0 | 5
2 | 0 | 1
3 | 1 | 7
4 | 5 | 6
5 | 5 | 12
6 | 13 | 2
7 | 13 | 3
8 | 2 | 8
9 | 3 | 8
10 | 3 | 9
11 | 14 | 3
12 | 14 | 4
13 | 4 | 10
14 | 4 | 11
query above will select nodes 0 and 13
I want to select at each iteration not only the nodes located on the right, but also the child and parent nodes, if they are not already in the cte.
For example, a query that should also select child nodes should start from node 0. Then at firts iteration select nodes 13, 5 and 1, at second iteration select nodes 2, 3, 12, 6, 7, at third iteration - nodes 8, 9 and at fourth iteration - node 10.
The query, which select at each iteration parents and childs, which not already in cte with neighbor right nodes at grid should select all nodes from picture at finish.
I tried to write the following query for select right nodes with their childs:
WITH RECURSIVE
cte(id, grid_x, grid_y) AS (
SELECT id, grid_x, grid_y
FROM nodes WHERE id = 0
UNION ALL
SELECT * FROM (
SELECT current.id, current.grid_x, current.grid_y
FROM nodes AS current, cte AS prev
WHERE current.grid_x = prev.grid_x + 1
AND current.grid_y = prev.grid_y
UNION
SELECT c.id, c.grid_x, c.grid_y
FROM nodes AS c, cte AS p, edges AS e
WHERE p.id = e.source AND c.id = e.target
AND here should be checking on existing node at cte
)
)
SELECT * FROM cte;
But recursive reference to query "cte" must not appear within a subquery
Query like this
WITH RECURSIVE
cte(id, grid_x, grid_y) AS (
SELECT id, grid_x, grid_y
FROM nodes WHERE id = 0
UNION ALL
SELECT current.id, current.grid_x, current.grid_y
FROM nodes AS current, edges AS e, cte AS prev
WHERE (current.grid_x = prev.grid_x + 1
AND current.grid_y = prev.grid_y)
OR (prev.id = e.source AND e.target = current.id)
)
SELECT * FROM cte;
But this query selects only node 0
Please, help me solve this problem.