# pgRouting Manual (3.1)

## pgr_bridges

`pgr_bridges` - Return the bridges of an undirected graph.

Boost Graph Inside

Availability

- Version 3.0.0

  - Return columns change: `seq` is removed

  - Official function

- Version 2.5.0

  - New experimental function

Support

- Supported versions: current(3.1) 3.0

- Unsupported versions: 2.6 2.5

## Description

A bridge is an edge of an undirected graph whose deletion increases its number of connected components. This implementation can only be used with an undirected graph.

The main characteristics are:

- The signature is for an undirected graph.

- The returned values are ordered:

  - edge ascending

- Running time: \(O(E * (V + E))\)

## Signatures

    pgr_bridges(Edges SQL)

    RETURNS SET OF (edge)
    OR EMPTY SET

Example

  The bridges of the graph

    SELECT * FROM pgr_bridges(
        'SELECT id, source, target, cost, reverse_cost FROM edge_table'
    );
     edge
    ------
        1
        6
        7
       14
       17
       18
    (6 rows)

## Parameters

Parameter | Type | Default | Description
--- | --- | --- | ---
Edges SQL | `TEXT` |  | Inner query as described below.

## Inner query

edges SQL

  an SQL query of an undirected graph, which should return a set of rows with the following columns:

Column | Type | Default | Description
--- | --- | --- | ---
id | `ANY-INTEGER` |  | Identifier of the edge.
source | `ANY-INTEGER` |  | Identifier of the first end point vertex of the edge.
target | `ANY-INTEGER` |  | Identifier of the second end point vertex of the edge.

cost

`ANY-NUMERICAL`

Weight of the edge (source, target)

- When negative: edge (source, target) does not exist, therefore it’s not part of the graph.

reverse_cost

`ANY-NUMERICAL`

-1

Weight of the edge (target, source),

- When negative: edge (target, source) does not exist, therefore it’s not part of the graph.

Where:

ANY-INTEGER

  SMALLINT, INTEGER, BIGINT

ANY-NUMERICAL

  SMALLINT, INTEGER, BIGINT, REAL, FLOAT

## Result Columns

Returns set of `(edge)`

Column | Type | Description
--- | --- | ---
edge | `BIGINT` | Identifier of the edge that is a bridge.

## See Also

- https://en.wikipedia.org/wiki/Bridge_%28graph_theory%29

- The queries use the Sample Data network.

Indices and tables

- Index

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