Question

Let’s imagine that we are having “cars” table with such a simple structure…

car_id INT
color ENUM('black','white','blue')
weight ENUM('light','medium','heavy')
type ENUM('van','sedan','limo')

Fist, I’m selecting car (1, black, heavy, limo), then I’d like to get list of related cars sorted by number of matching columns (without any column weight). So, first I’m expecting to see (black, heavy, limo) cars, then I’m expecting to see cars with only 2 matching fields etc.

Is it possible to execute this kind of sorting using SQL?

Sorry for my English, but I really hope that my question is clear for you.

Thank you.

Answer 1

There are probably a few ways to optimise the sub-queries, but without using case statements or sub-optimal join clauses:

select
        *
    from
        (
            select
                    selection.CarId,
                    selection.Colour,
                    selection.Weight,
                    selection.Type,
                    3 as Relevance
                from
                    tblCars as selection
                where
                    selection.Colour = 'black' and selection.Weight = 'light' and selection.Type = 'van'
            union all
            select
                    cars.CarId,
                    cars.Colour,
                    cars.Weight,
                    cars.Type,
                    count(*) as Relevance
                from
                    tblCars as cars
                inner join
                    (
                        select
                                byColour.CarId
                            from
                                tblCars as cars
                            inner join
                                tblCars as byColour
                            on
                                cars.Colour = byColour.Colour
                            where
                                cars.Colour = 'black' and cars.Weight = 'light' and cars.Type = 'van'
                                and
                                byColour.CarId <> cars.CarId
                        union all
                        select
                                byWeight.CarId
                            from
                                tblCars as cars
                            inner join
                                tblCars as byWeight
                            on
                                cars.Weight = byWeight.Weight
                            where
                                cars.Colour = 'black' and cars.Weight = 'light' and cars.Type = 'van'
                                and
                                byWeight.CarId <> cars.CarId
                        union all
                        select
                                byType.CarId
                            from
                                tblCars as cars
                            inner join
                                tblCars as byType
                            on
                                cars.Type = byType.Type
                            where
                                cars.Colour = 'black' and cars.Weight = 'light' and cars.Type = 'van'
                                and
                                byType.CarId <> cars.CarId
                    ) as matches
                on
                    cars.CarId = matches.CarId
                group by
                    cars.CarId,
                    cars.Colour,
                    cars.Weight,
                    cars.Type
        ) as results
    order by
        Relevance desc

Output:

CarId   Colour  Weight  Type    Relevance
1       black   light   van     3
3       white   light   van     2
4       blue    light   van     2
5       black   medium  van     2
6       white   medium  van     1
7       blue    medium  van     1
8       black   heavy   limo    1