pgr_strongComponents  pgRouting Manual (3.3)
pgr_strongComponents
pgr_strongComponents
 Strongly connected components of a directed graph using Tarjan’s algorithm based on DFS.
Availability

Version 3.0.0

Return columns change:

n_seq
is removed 
seq
changed type toBIGINT


Official function


Version 2.5.0

New experimental function

Description
A strongly connected component of a directed graph is a set of vertices that are all reachable from each other.
The main characteristics are:

The signature is for a directed graph.

Components are described by vertices

The returned values are ordered:

component ascending

node ascending


Running time: \(O(V + E)\)
Signatures
pgr_strongComponents(Edges SQL)
RETURNS SET OF (seq, component, node)
OR EMPTY SET
 Example :

The strong components of the graph
SELECT * FROM pgr_strongComponents(
'SELECT id, source, target, cost, reverse_cost FROM edge_table'
);
seq component node
++
1 1 1
2 1 2
3 1 3
4 1 4
5 1 5
6 1 6
7 1 7
8 1 8
9 1 9
10 1 10
11 1 11
12 1 12
13 1 13
14 14 14
15 14 15
16 16 16
17 16 17
(17 rows)
Parameters
Parameter 
Type 
Default 
Description 

Edges SQL 

Inner query as described below. 
Inner query
 edges SQL :

an SQL query of a directed graph, which should return a set of rows with the following columns:
Column 
Type 
Default 
Description 

id 

Identifier of the edge. 

source 

Identifier of the first end point vertex of the edge. 

target 

Identifier of the second end point vertex of the edge. 

cost 

Weight of the edge (source, target)


reverse_cost 

1 
Weight of the edge (target, source) ,

Where:
 ANYINTEGER :

SMALLINT, INTEGER, BIGINT
 ANYNUMERICAL :

SMALLINT, INTEGER, BIGINT, REAL, FLOAT
Result Columns
Returns set of
(seq,
component,
node)
Column 
Type 
Description 

seq 

Sequential value starting from 1 . 
component 

Component identifier. It is equal to the minimum node identifier in the component. 
node 

Identifier of the vertex that belongs to component . 
See Also

The queries use the Sample Data network.

Boost: Strong components

wikipedia: Strongly connected component
Indices and tables