pgr_topologicalSort  Experimental¶
pgr_topologicalSort
— Returns the linear ordering of the vertices(s) for weighted directed acyclic graphs(DAG).
In particular, the topological sort algorithm implemented by Boost.Graph.
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 3.0.0
New experimental function
Support
Description¶
The topological sort algorithm creates a linear ordering of the vertices such that if edge (u,v) appears in the graph, then v comes before u in the ordering.
This implementation can only be used with a directed graph with no cycles i.e. directed acyclic graph.
 The main characteristics are:
Process is valid for directed acyclic graphs only. otherwise it will throw warnings.
For optimization purposes, if there are more than one answer, the function will return one of them.
The returned values are ordered in topological order:
Running time: \(O( (V + E))\)
Signatures¶
Summary
pgr_topologicalSort(edges_sql)
RETURNS SET OF (seq, sorted_v)
OR EMPTY SET
 Example
For a directed graph
SELECT * FROM pgr_topologicalsort(
'SELECT id,source,target,cost,reverse_cost FROM edge_table1'
);
seq  sorted_v
+
1  0
2  1
3  3
4  2
(4 rows)
Parameters¶
Parameter 
Type 
Default 
Description 

edges_sql 

SQL query as described above. 
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 

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, sorted_v)
Column 
Type 
Description 

seq 

Sequential value starting from 1. 
sorted_v 

Linear ordering of the vertices(ordered in topological order) 