pgr_kruskal
¶
pgr_kruskal
— Minimum spanning tree of a graph using Kruskal’s algorithm.
Availability
Version 3.0.0
New Official function
Description¶
This algorithm finds the minimum spanning forest in a possibly disconnected graph using Kruskal’s algorithm.
The main Characteristics are:
It’s implementation is only on undirected graph.
Process is done only on edges with positive costs.
When the graph is connected
The resulting edges make up a tree
When the graph is not connected,
Finds a minimum spanning tree for each connected component.
The resulting edges make up a forest.
The total weight of all the edges in the tree or forest is minimized.
Kruskal’s running time: \(O(E * log E)\)
EMPTY SET is returned when there are no edges in the graph.
Signatures¶
Summary
(edge, cost)
 Example:
Minimum spanning forest
SELECT * FROM pgr_kruskal(
'SELECT id, source, target, cost, reverse_cost
FROM edges ORDER BY id'
) ORDER BY edge;
edge  cost
+
1  1
2  1
3  1
6  1
7  1
10  1
11  1
12  1
13  1
14  1
15  1
16  1
17  1
18  1
(14 rows)
Parameters¶
Parameter 
Type 
Description 


Edges SQL as described below. 
Inner Queries¶
Edges SQL¶
Column 
Type 
Default 
Description 


ANYINTEGER 
Identifier of the edge. 


ANYINTEGER 
Identifier of the first end point vertex of the edge. 


ANYINTEGER 
Identifier of the second end point vertex of the edge. 


ANYNUMERICAL 
Weight of the edge ( 


ANYNUMERICAL 
1 
Weight of the edge (

Where:
 ANYINTEGER:
SMALLINT
,INTEGER
,BIGINT
 ANYNUMERICAL:
SMALLINT
,INTEGER
,BIGINT
,REAL
,FLOAT
Result columns¶
Returns set of (edge, cost)
Column 
Type 
Description 



Identifier of the edge. 


Cost to traverse the edge. 
See Also¶
The queries use the Sample Data network.
Indices and tables