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Introduction
The very basics
Infinite looping
Processing trees with recursive CTEs
Processing graphs with recursive ctes
26. Graphs in computer science
Summary

## Instruction

Well done! Since you already know how to tackle hierarchical structures represented in the form of trees, it's time to move on and introduce the second type of real-world situation that we can tackle with recursive CTEs: graphs.

Graphs consists of vertices and edges. In real life, graphs can often correspond to road maps. Take a look:

In a database, we may store vertices (cities) in one table, and edges (the roads between them cities) in another table:

City
Name
London
Cambridge
...
Road
NameFrom NameTo DistanceKM
London Cambridge 78
...

For educational purposes, we will simplify things a bit. We will only use a single table, City, with city names and GPS coordinates and we'll assume that you can go directly from one city to another.

First, let's take a look at this table.

## Exercise

Select all data from the City table.

The table contains the following columns:

• Name – the name of the city,
• Lat – the latitude of the city,
• Lon – the longitude of the city.

The last two columns indicates coordinates. Based on those coordinates, we will calculate the distance between two cities in a straight line and treat it as the distance.