# OQGRAPH Examples

### Contents

## Creating a table with origid, destid only

CREATE TABLE oq_backing ( origid INT UNSIGNED NOT NULL, destid INT UNSIGNED NOT NULL, PRIMARY KEY (origid, destid), KEY (destid) );

Some data can be inserted into the backing table to test with later:

INSERT INTO oq_backing(origid, destid) VALUES (1,2), (2,3), (3,4), (4,5), (2,6), (5,6);

Now the read-only OQGRAPH table is created. The CREATE statement must match the format below - any difference will result in an error.

CREATE TABLE oq_graph ( latch VARCHAR(32) NULL, origid BIGINT UNSIGNED NULL, destid BIGINT UNSIGNED NULL, weight DOUBLE NULL, seq BIGINT UNSIGNED NULL, linkid BIGINT UNSIGNED NULL, KEY (latch, origid, destid) USING HASH, KEY (latch, destid, origid) USING HASH ) ENGINE=OQGRAPH data_table='oq_backing' origid='origid' destid='destid';

## Creating a table with weight

For the examples on this page, we'll create a second OQGRAPH table and backing table, this time with `weight`

as well.

CREATE TABLE oq2_backing ( origid INT UNSIGNED NOT NULL, destid INT UNSIGNED NOT NULL, weight DOUBLE NOT NULL, PRIMARY KEY (origid, destid), KEY (destid) );

INSERT INTO oq2_backing(origid, destid, weight) VALUES (1,2,1), (2,3,1), (3,4,3), (4,5,1), (2,6,10), (5,6,2);

CREATE TABLE oq2_graph ( latch VARCHAR(32) NULL, origid BIGINT UNSIGNED NULL, destid BIGINT UNSIGNED NULL, weight DOUBLE NULL, seq BIGINT UNSIGNED NULL, linkid BIGINT UNSIGNED NULL, KEY (latch, origid, destid) USING HASH, KEY (latch, destid, origid) USING HASH ) ENGINE=OQGRAPH data_table='oq2_backing' origid='origid' destid='destid' weight='weight';

## Shortest Path

A `latch`

value of `'dijkstras'`

and an `origid`

and `destid`

is used for finding the shortest path between two nodes, for example:

SELECT * FROM oq_graph WHERE latch='breadth_first' AND origid=1 AND destid=6; +----------+--------+--------+--------+------+--------+ | latch | origid | destid | weight | seq | linkid | +----------+--------+--------+--------+------+--------+ | dijkstras| 1 | 6 | NULL | 0 | 1 | | dijkstras| 1 | 6 | 1 | 1 | 2 | | dijkstras| 1 | 6 | 1 | 2 | 6 | +----------+--------+--------+--------+------+--------+

Note that nodes are uni-directional, so there is no path from node 6 to node 1:

SELECT * FROM oq_graph WHERE latch='dijkstras' AND origid=6 AND destid=1; Empty set (0.00 sec)

Using the GROUP_CONCAT function can produce more readable results, for example:

SELECT GROUP_CONCAT(linkid ORDER BY seq) AS path FROM oq_graph WHERE latch='dijkstras' AND origid=1 AND destid=6; +-------+ | path | +-------+ | 1,2,6 | +-------+

Using the table `oq2_graph`

, the shortest path is different:

SELECT GROUP_CONCAT(linkid ORDER BY seq) AS path FROM oq2_graph WHERE latch='dijkstras' AND origid=1 AND destid=6; +-------------+ | path | +-------------+ | 1,2,3,4,5,6 | +-------------+

The reason is the weight between nodes 2 and 6 is `10`

in `oq_graph2`

, so the shortest path taking into account `weight`

is now across more nodes.

## Possible destinations

SELECT GROUP_CONCAT(linkid) AS dests FROM oq_graph WHERE latch='dijkstras' AND origid=2; +-----------+ | dests | +-----------+ | 5,4,6,3,2 | +-----------+

Note that this returns all possible destinations along the path, not just immediate links.

## Summary of Implemented latch commands

Latch | Alternative | additional where clause fields | Graph operation |
---|---|---|---|

NULL | (unspecified) | (none) | List original data |

(empty string) | 0 | (none extra) | List all vertices in linkid column |

(empty string) | 0 | origid | List all first hop vertices from origid in linkid column |

dijkstras | 1 | origid, destid | Find shortest path using Dijkstras algorithm between origid and destid, with traversed vertex ids in linkid column |

dijkstras | 1 | origid | Find all vertices reachable from origid, listed in linkid column, and report sum of weights of vertices on path to given vertex in weight |

dijkstras | 1 | destid | Find all vertices reachable from destid, listed in linkid column, and report sum of weights of vertices on path to given vertex in weight |

breadth_first | 2 | origid | List vertices reachable from origid in linkid column |

breadth_first | 2 | destid | List vertices from which a path can be found to destid in linkid column |

breadth_first | 2 | origid, destid | Visit all vertices possible between origid and destid, report in linkid column |

Note: the use of integer latch commands is deprecated and may be phased out in a future release. Currently, numeric values in the strings are interpeted as aliases, and use of an integer column can be optionally allowed, for the latch commands column.

The use of integer latches is controlled using the oqgraph_allow_create_integer_latch system variable.