sql server graph query, find all paths to node

Question

I have a very common problem I am trying to solve using graph queries (sql server 2017).

I want to build a query and find how anyone in the nodes is connected to C.
I want to build a query and find how anyone in the nodes is connected to C (with 1 or 2 connections).

here is the full script to create this graph:

DROP TABLE IF EXISTS Person;
CREATE TABLE Person (userName VARCHAR(100)  PRIMARY KEY) AS NODE;

INSERT INTO Person (userName) VALUES ('A'),('B'),('C'),('D'),('E'),('F'); 

DROP TABLE IF EXISTS Follow; 
CREATE TABLE Follow AS EDGE;

INSERT INTO Follow ($from_id, $to_id) VALUES (
   (SELECT $node_id FROM dbo.Person WHERE userName = 'A'),
   (SELECT $node_id FROM dbo.Person WHERE userName = 'E')),

   ((SELECT $node_id FROM dbo.Person WHERE userName = 'E'),
   (SELECT $node_id FROM dbo.Person WHERE userName = 'C')),


   ((SELECT $node_id FROM dbo.Person WHERE userName = 'C'),
   (SELECT $node_id FROM dbo.Person WHERE userName = 'A')),


   ((SELECT $node_id FROM dbo.Person WHERE userName = 'A'),
   (SELECT $node_id FROM dbo.Person WHERE userName = 'F')),

   ((SELECT $node_id FROM dbo.Person WHERE userName = 'F'),
   (SELECT $node_id FROM dbo.Person WHERE userName = 'B')),

   ((SELECT $node_id FROM dbo.Person WHERE userName = 'B'),
   (SELECT $node_id FROM dbo.Person WHERE userName = 'F')),

   ((SELECT $node_id FROM dbo.Person WHERE userName = 'B'),
   (SELECT $node_id FROM dbo.Person WHERE userName = 'E')),

   ((SELECT $node_id FROM dbo.Person WHERE userName = 'E'),
   (SELECT $node_id FROM dbo.Person WHERE userName = 'B'));

this query is not working since it is giving me only the direct relation:

SELECT Person1.userName as userName1, Person2.userName as userName2   
FROM Person as Person1, Follow, Person as Person2 
WHERE MATCH(Person1-(Follow)->Person2)
AND Person2.userName = 'C'

For sql 2017 you'll have to use a recursive cte. For sql 2019 you could use the answer provided by satishcse — lptr, Jan 08 '20 at 08:44
@lptr could you pls share how to do it with cte? I have sql 2017. Much appreciated! — DmitriBodiu, Apr 03 '20 at 18:01

sacse · Answer 1 · 2021-09-16T11:36:14.873

you can try something like below:

SELECT 
        p1.userName, 
        p1.userName as StartNode,
        LAST_VALUE(p2.userName) WITHIN GROUP (GRAPH PATH) AS FinalNode,
        STRING_AGG(p2.userName,'->') WITHIN GROUP (GRAPH PATH) AS [Edges Path],
        COUNT(p2.userName) WITHIN GROUP (GRAPH PATH) AS Levels
    FROM
        dbo.Person p1,
        dbo.Person FOR PATH p2,
        dbo.Follow FOR PATH Follow
    WHERE 
        MATCH(SHORTEST_PATH(p1(-(Follow)->p2)+))
        AND p1.userName = 'C';

to find all the incoming connection for a node, we need to wrap the query and filter for the final node like below:

SELECT
    username, StartNode, [Edges Path], FinalNode, Levels
FROM (
    SELECT 
        P1.username, 
        P1.username as StartNode, 
        STRING_AGG(P2.userName,'->') WITHIN GROUP (GRAPH PATH) AS [Edges Path],
        LAST_VALUE(P2.userName) WITHIN GROUP (GRAPH PATH) AS FinalNode,
        COUNT(P2.userName) WITHIN GROUP (GRAPH PATH) AS Levels
    FROM
        Person P1,
        Person FOR PATH P2,
        Follow FOR PATH Follow
    WHERE 
        MATCH(SHORTEST_PATH(P1(-(Follow)->P2)))
 ) AS Q
 WHERE Q.FinalNode = 'C'

to limit the levels or the number of hops, we can provide the recursion quantifiers in place of (+ --- one or more) like below:

SELECT
    username, StartNode, [Edges Path], FinalNode, Levels
FROM (
    SELECT 
        P1.username, 
        P1.username as StartNode, 
        STRING_AGG(P2.userName,'->') WITHIN GROUP (GRAPH PATH) AS [Edges Path],
        LAST_VALUE(P2.userName) WITHIN GROUP (GRAPH PATH) AS FinalNode,
        COUNT(P2.userName) WITHIN GROUP (GRAPH PATH) AS Levels
    FROM
        Person P1,
        Person FOR PATH P2,
        Follow FOR PATH Follow
    WHERE 
        MATCH(SHORTEST_PATH(P1(-(Follow)->P2){1,3}))
 ) AS Q
 WHERE Q.FinalNode = 'C'

Thank you and sorry for the late reply. I had problems installing SQL server 2019. Any in your query you are showing all `C` outgoing connections. I also want to know all `C` incoming connections.for example: `A->E->C` or `F->B->E->C` possible? I dont mind to have multiple queries. thanks — SexyMF, Jan 20 '20 at 14:22
DBFiddle Link for above great example: https://dbfiddle.uk/?rdbms=sqlserver_2019l&fiddle=6145b8352baa7589f7be0bf1d7de8468 — Sanora, Dec 01 '21 at 21:12

sql server graph query, find all paths to node

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