MySQL how to select multiple attributes from a Cartesian product? - mysql

Question

I'm trying to get multiple attributes (e.g bedrooms, bathrooms, etc) from a few tables yes I can only seem to get one attribute with my current query. What am I missing?
What I am ultimately trying to find is property_id's with 2 bathrooms and 2 bedrooms. In this case, my desired results are property id's 1 and 4.
Here's my example on sqlfiddle
Example tables:
property
--------
id
1
2
3
4
attribute
---------
id name
1 bedrooms
2 bathrooms
attribute_value
---------------------
id attribute_id value
1 1 1
2 1 2
3 1 3
4 2 1
5 2 2
6 2 3
property_attributes
------------------------------
property_id attribute_value_id
1 2
1 5
2 2
2 4
3 1
3 4
4 2
4 5
This query can produce the results I want if I only want to see a query based on single attribute:
SELECT p.property_id
FROM property p
INNER JOIN property_attribute pa ON p.property_id = pa.property_id
INNER JOIN property_area pc ON p.property_id = pc.property_id
WHERE pa.attribute_value_id
IN (
SELECT av.attribute_value_id
FROM attribute_value av
INNER JOIN attribute a ON av.attribute_id = a.attribute_id
WHERE a.name like 'bedrooms' AND av.value like '2')
But what must I do to get results with more attributes (e.g. WHERE a.name like 'bathrooms' AND av.value like '2')? If I add another subquery in the main where clause, it doesn't return any results.
/// EDIT ///
here is the solution that worked for me if anyone else winds up in such a situation:
SELECT p.property_id
FROM property p
INNER JOIN property_attribute pa ON p.property_id = pa.property_id
INNER JOIN property_attribute pa2 ON p.property_id = pa2.property_id
INNER JOIN property_attribute pa3 ON p.property_id = pa3.property_id
WHERE pa.attribute_value_id = 2
AND pa2.attribute_value_id = 5
AND pa3.attribute_value_id = 7
This makes usage of a self-join.

Answer 1

You have an awful lot of indirection in your schema. Is there any particular point why you need the property_attribute table? Do you expect a single attribute value to be shared by many properties?
In any case, here is the query for you. Very much in the spirit of the two possible duplicates I mentioned above.
SELECT property.property_id,
bedrooms.value AS bedrooms,
bathrooms.value AS bathrooms
FROM property,
attribute AS bedrooms_attr,
attribute_value AS bedrooms,
property_attribute AS bedrooms_prop,
attribute AS bathrooms_attr,
attribute_value AS bathrooms,
property_attribute AS bathrooms_prop
WHERE bedrooms_attr.name = 'bedrooms'
AND bedrooms.attribute_id = bedrooms_attr.attribute_id
AND bedrooms.attribute_value_id = bedrooms_prop.attribute_value_id
AND bedrooms_prop.property_id = property.property_id
AND bedrooms.value = 2
AND bathrooms_attr.name = 'bathrooms'
AND bathrooms.attribute_id = bathrooms_attr.attribute_id
AND bathrooms.attribute_value_id = bathrooms_prop.attribute_value_id
AND bathrooms_prop.property_id = property.property_id
AND bathrooms.value = 2
Thanks for providing a fiddle with data to play with.