4 Tables SQL Join Problem

Question

I have four tables like the following:

Cars:
car_id | make_id
1      | 1
2      | 3

Cars Makes 
make_id  | make_name
1        | BMW
2        | Ferrari
3        | Mercedes 


Car Properties 
car_id  | property_id | property_value
1       | 1           | Automatic
1       | 2           | 1000
1       | 3           | Diesel
2       | 1           | Manual
2       | 2           | 15000
2       | 3           | Gasoline

Properties
property_id | property_name
1           | Transmission
2           | Mileage
3           | Fuel

As you can see, every car has a make_id from the table "Makes".

And There is a separate table contains All the main properties of the cars. Then there is "Car Properties" table which contain the car_id, property_id, property_value

Now i want to make the following query: get the BMW cars with automatic transmission and the mileage is 1000 with diesel fuel. let's suppose that the form can provide the following: make_id = 1 (BMW) properties = Automatic,1000,Diesel

PS: It will be okay if i just get the result car_id

Answer 1

Not 100% on the mysql syntax (sorry live too much in TSQL) but this is the relationship idea to use.

FROM Car 
JOIN CarProperties Trans
    ON Car.car_id = Trans.CarID AND Trans.property_id = 1
JOIN CarProperties Mileage 
    ON Car.car_id = Mileage.CarID AND Mileage.property_id = 2
JOIN CarProperties Fuel 
    ON Car.car_id = Fuel.CarID AND Fuel.property_id = 3

Your select can draw from mileage, fuel or trans, as can your where clause

Answer 2

Assuming the query needs to satisfy all three properties:

SELECT c.car_id
FROM
    Cars c INNER JOIN (
        SELECT car_id, COUNT(*) AS prop_count
        FROM
            CarProperties
        WHERE
            (property_id = 1 AND property_value = 'Automatic')
            OR (property_id = 2 AND property_value = '1000')
            OR (property_id = 3 AND property_value = 'Diesel')
        GROUP BY car_id
    ) AS cp ON c.car_id = cp.car_id AND cp.prop_count = 3
WHERE
    c.make_id = 1;

Then it occurred to me:

SELECT c.car_id
FROM
    Cars c INNER JOIN (
        SELECT car_id FROM CarProperties
        WHERE property_id = 1 AND property_value = 'Automatic'
    ) AS t ON c.car_id = t.car_id INNER JOIN (
        SELECT car_id FROM CarProperties
        WHERE property_id = 2 AND property_value = '1000'
    ) AS m ON c.car_id = m.car_id INNER JOIN (
        SELECT car_id FROM CarProperties
        WHERE property_id = 3 AND property_value = 'Diesel'
    ) AS f ON c.car_id = f.car_id
WHERE
   c.make_id = 1;

Answer 3

Since the input only has values like "Automatic,1000,Diesel" and none like "Transmission,Mileage,Fuel", you will have to ignore the properties table and pray that your property types never include overlapping keys (or more than one numeric type). Also, since the input already has the make_id directly we can leave off the Cars Makes table as well.

The other trick here is that you can join to the same table more than once.

SELECT c.car_id 
FROM cars c
INNER JOIN `Car Properties` cp1 
    ON cp1.car_id = c.car_id AND cp1.property_value = 'Automatic'
INNER JOIN `Car Properties` cp2 
    ON cp2.car_id = c.car_id AND cp2.property_value = 'Diesel'
INNER JOIN `Car Properties` cp3 
    ON cp3.car_id = c.car_id  AND cp3.property_value = '1000'

Answer 4

you can join Car Properties and Properties first, give it an alias and get the car_id array, then search Cars join Cars Makes "IN" (car_id_array).

Answer 5

Perhaps this might work:

SELECT car_id
FROM Cars LEFT JOIN CarMakes USING (make_id)
     JOIN (SELECT car_id
           FROM CarProperties JOIN Properties USING (property_id)
           WHERE property_name='Transmission' AND property_value='Automatic') a
     JOIN (SELECT car_id
           FROM CarProperties JOIN Properties USING (property_id)
           WHERE property_name='Mileage' AND property_value='1000') b
     JOIN (SELECT car_id
           FROM CarProperties JOIN Properties USING (property_id)
           WHERE property_name='Fuel' AND property_value='Diesel') c
WHERE make_name = 'BMW'

Answer 6

select cars.car_id
   from
      cars 
         join `car properties` cp
            on cars.car_id = cp.car_id
            join properties p
               on cp.property_id = p.property_id
   where
         cars.make_id = 1
      and (   ( p.property_name = "Transmission" and cp.property_Value = "Automatic" )
           OR ( p.property_name = "Mileage" and cp.property_Value = "1000" )
           OR ( p.property_name = "Fuel" and cp.property_Value = "Diesel" )
          )
   group by
      cars.car_id
   having
      count(*) = 3