How to group/List all nodes of a undirected graph using teradata sql

问题

I have data for many diff. set of undirected graphs in a table (like adjacent list relationship, one node is connected which all node) and I need to group all individual undirected graphs.

Eg: all nodes of the particular undirected graphs will be in a group & group name will be the min. of the node.

sel d.adj_node, min(d.adj_node) Over (Partition By a.node) as grp
table a 
left join table b
on a.adj_node=b.node
left join table c
on b.adj_node=c.node
left join table d
on c.adj_node=d.node;

Now, I am doing a self-join for 4,5 times and then on top that query doing partitioning it to get the desired output. But doing self-join 4 5 times is creating performance issue.

So, need some recursive sql, stored procedure or some other logic to do the same for all levels. Input Data & Required Output will be like this link Looking for some suggestions.

Input Table

node    adj_node
1       2
2       1
2       3
2       5
2       6
2       7
3       2
3       4
4       3
4       5
4       6
4       7
5       2
5       4
6       2
6       4
6       8
7       2
7       4
8       6
1       1
2       2
3       3
4       4
5       5
6       6
7       7
8       8
10      11
11      10
11      13
11      14
12      13
12      14
13      11
13      12
13      14
14      11
14      12
14      13
10      10
11      11
12      12
13      13
14      14


Output
node    grp
1       1
2       1
3       1
4       1
5       1
6       1
7       1
8       1
10      10
11      10
12      10
13      10
14      10

回答1:

I just remembered that I did something similar before using updates on a temp table.

The best way to implement this would be a Stored Procedure with a loop in it:

CREATE VOLATILE TABLE vt_tab AS
 (
   SELECT DISTINCT NODE , adj_node, NODE AS grp
   FROM tab AS t1
   WHERE adj_node <> NODE
 ) WITH DATA
ON COMMIT PRESERVE ROWS
;

-- REPEAT this update UNTIL activity_count = 0
UPDATE vt_tab FROM
 ( 
  SELECT t2.NODE, MIN(t1.grp) AS mingrp
  FROM vt_tab AS t1 JOIN vt_tab AS t2
  ON t1.adj_node = t2.NODE
  AND t1.grp < t2.grp
  GROUP BY t2.NODE
 ) x
SET grp = mingrp
WHERE vt_tab.NODE = x.NODE
;

--get the final result
SEL DISTINCT NODE,grp
FROM vt_tab
ORDER BY 1
;

Recursion might be possible, but there's a high probability that it will blow your spool because you need repeated m:n joins and only the final Select allows to reduce the result rows.

回答2:

A solution with a recursive CTE:

with cte as
(
    select node as node, node as grp
    from Tabl_1
    Union all
    select C.node, T.adj_node
    from CTE C inner join Tabl_1 T on C.grp = T.node
    where T.adj_node < C.grp
)

select node, MIN(grp) as grp 
from cte
group by node
order by node

== EDIT 1 == Here is a new version to reflect your point.

with cte as
(
    select node as node, node as grp, ',' + CAST(node as varchar(max)) + '-' + CAST(node as varchar(max)) + ',' as pair
    from Tabl_1
    Union all
    select C.node, T.adj_node, C.pair + CAST(C.node as varchar(max)) + '-' + CAST(T.adj_node as varchar(max)) + ','
    from CTE C inner join Tabl_1 T on C.grp = T.node
    where C.pair not like '%,' + CAST(C.node as varchar(max)) + '-' + CAST(T.adj_node as varchar(max)) + ',%'
)

select node, MIN(grp) as grp 
from cte
group by node
order by node

来源：https://stackoverflow.com/questions/35474393/how-to-group-list-all-nodes-of-a-undirected-graph-using-teradata-sql

标签

sql

stored-procedures

teradata

recursive-query

undirected-graph