Travel planning for flight data

Hierarchical and Recursive Queries in SQL Server

Jasmin Ludolf

Content Developer

Scoreboard of an airport

Example Scoreboard of an airport

How is a flight data set structured?

Departure	Arrival	FlightNumber	Cost	Time
London	Paris	LH3827	90	2
Vienna	New York	MH2370	379	8
New York	Paris	LH9832	489	9
Vienna	Paris	SU2389	200	3
London	Chicago	OP1230	650	10
New York	Chicago	NL5460	150	2

How to build a flight route?

An image about all possible flight routes over the world

Use recursion to get all possible flight routes
A route is defined by the departure airport and the destination airport
Limit the number of possible layovers to create realistic flight routes

Building a flight route - step 1

WITH flightRoute (Departure, Arrival, stops) AS(
  -- Anchor query
  SELECT f.Departure,f.Arrival, 0
      FROM flightPlan f
      WHERE Departure = 'Vienna'
  -- Recursive query
  UNION ALL
      SELECT p.Departure, f.Arrival, p.stops + 1
      FROM flightPlan f, flightRoute p
      WHERE p.Arrival = f.Departure AND 
        p.stops < 5 
)

SELECT Departure, Arrival, stops
    FROM flightRoute

+-----------+---------------+--------+
| Departure | Arrival       | stops  |
|-----------|---------------|--------|
| Vienna    | Paris         | 2      |
| Vienna    | San Francisco | 3      |
| Vienna    | Vienna        | 3      |
| Vienna    | Frankfurt     | 3      |
| ...       | ...           | ...    |
+-----------+---------------+--------+

Building a flight route - step 2

WITH flightRoute (Departure, Arrival, stops, route) AS(
  SELECT f.Departure, f.Arrival, 0, 
  CAST(Departure + '->' + Arrival AS VARCHAR(MAX))
      FROM flightPlan f
      WHERE Departure = 'Vienna'

  UNION ALL
  SELECT p.Departure, f.Arrival, p.stops + 1, 
  p.totalCost + f.Cost, 
  CAST(p.route + '->' + f.Arrival AS VARCHAR(MAX))
      FROM flightPlan f, flightRoute p

      WHERE p.Arrival = f.Departure AND p.stops < 5
)

Introduce route in the anchor member
Track routes in recursive member
Limit the number of stops

Building a flight route - result

SELECT Departure, Arrival, Route
    FROM flightRoute

+-----------+--------------+-------------------------------------------+
| Departure | Arrival      | route                                     |
|-----------|--------------|-------------------------------------------+
| London    | New York     | London -> Vienna -> Chicago -> New York   |
| Vienna    | Chicago      | Vienna -> London -> Chicago               |        
| Paris     | Los Angeles  | Paris -> Toronto -> Los Angeles           |
| Chicago   | New York     | Chicago -> New York                       |
| Rome      | New York     | Rome -> London -> Chicago -> New York     |    
| ...       | ...          | ...                                       |
+-----------+--------------+-------------------------------------------+

Querying for possible flight with limits

WITH flightRoute (Departure, Arrival, stops, totalCost, route) AS(
  SELECT f.Departure, f.Arrival, 0, Cost,
    CAST(Departure + '->' + Arrival AS NVARCHAR(MAX))
      FROM flightPlan f
      WHERE Departure = 'New York'
  UNION ALL
  SELECT  p.Departure, f.Arrival, p.stops+1, 
  p.totalCost + f.Cost, p.route + '->' + f.Arrival
      FROM flightPlan f, flightRoute p
      WHERE p.Arrival = f.Departure AND p.stops < '...' 
)

SELECT '...'    
    FROM flightRoute
    WHERE '...' ;

Find all possible destination airports where:

The departure airport is fixed
- New York
The number of stops is limited to n
The output is limited by a condition
- cost limit
- cheapest route to some destination

Let's find possible flight routes!

Hierarchical and Recursive Queries in SQL Server