Aravimdan_3. The distinct only works when the 2 columns are unique. Distinct is made to avoid duplicate, but in order to work all the selected combined columns must be unique. Therefore London to Paris is unique within its own row, and Paris to London is unique with its own row. GPS systems uses kinda the same system but in order to work you must specify the From Location to Destination Location. If the trips a round trip you have then to invert the locations in order to work, cuz your first trip might be shorter then your returning trip and your returning trip might take you to different roads.

your locations are stored in one table only?