pgr_makeConnected  Experimental¶
pgr_makeConnected
— Returns the set of edges that will make the graph connected.
Warning
Possible server crash
These functions might create a server crash
Warning
Experimental functions
They are not officially of the current release.
They likely will not be officially be part of the next release:
The functions might not make use of ANYINTEGER and ANYNUMERICAL
Name might change.
Signature might change.
Functionality might change.
pgTap tests might be missing.
Might need c/c++ coding.
May lack documentation.
Documentation if any might need to be rewritten.
Documentation examples might need to be automatically generated.
Might need a lot of feedback from the comunity.
Might depend on a proposed function of pgRouting
Might depend on a deprecated function of pgRouting
Availability
Version 3.2.0
New experimental function
Description¶
Adds the minimum number of edges needed to make the input graph connected. The algorithm first identifies all of the connected components in the graph, then adds edges to connect those components together in a path. For example, if a graph contains three connected components A, B, and C, make_connected will add two edges. The two edges added might consist of one connecting a vertex in A with a vertex in B and one connecting a vertex in B with a vertex in C.
 The main characteristics are:
It will give the minimum list of all edges which are needed in the graph to make the graph connected.
Applicable only for undirected graphs.
The algorithm does not considers traversal costs in the calculations.
Running time: \(O(V + E)\)
Signatures¶
Summary
pgr_makeConnected(Edges SQL)
RETURNS SET OF (seq, start_vid, end_vid)
OR EMPTY SET
 Example
Query done on Sample Data network gives the list of edges that are needed in the graph to make it connected.
SELECT * FROM pgr_makeConnected(
'SELECT id, source, target, cost, reverse_cost
FROM edge_table'
);
seq  start_vid  end_vid
++
1  13  14
2  15  16
(2 rows)
Parameters¶
Parameter 
Type 
Default 
Description 

Edges SQL 

SQL query as described below. 
Inner query¶
 Edges SQL
an SQL query, 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 



reverse_cost 

1 

Where:
 ANYINTEGER
SMALLINT, INTEGER, BIGINT
 ANYNUMERICAL
SMALLINT, INTEGER, BIGINT, REAL, FLOAT
Result Columns¶
Returns set of (seq, start_vid, end_vid)
Column 
Type 
Description 

seq 

Sequential value starting from 1. 
start_vid 

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

Identifier of the second end point vertex of the edge. 
See Also¶
The queries use the Sample Data network.
Indices and tables