This advanced SQL exercise is part of the book: Advanced SQL – Practical Techniques and Use-Cases, which includes 100 day-to-day SQL challenges (and solutions), need-to-know advanced features, and key concepts.
 

A GPS-based geographical navigation application, manages a table that specifies distances between various destinations. Each row in this table indicates a serial number, starting point, destination, and distance. For example, the distance between point A and point C is 23 kilometers.


CREATE TABLE distances
(distance_id int identity(1,1),
from_d  varchar(25),
to_d    varchar(25),
distance int)
GO

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