Hi,
As you mentioned that you have given options to search, so I think its very easy to implement View All functionality.
Its totally depends on the select query.
In your select query remove where condition or add all options in where condition then all results will be displayed.
For example if you have given
1)Bus
2)Bike
3)Car
in the options for the user to search then
IF user selects
Bike
in the option then your query would look like
SELECT * FROM VehicleDatabase WHERE VehilceType = 'Bike';
Now if you want to select all then your query would look like
SELECT * FROM VehicleDatabase WHERE VehilceType in ('Bike','Bus','Car');
Note: Datatype and fields are depends on your Database table.
Hope this helps you a bit.
Regards,
RK