Question

I am trying to figure out a way to query a property feature lookup table.

I have a property table that contains rental property information (address, rent, deposit, # of bedrooms, etc.) along with another table (Property_Feature) that represents the features of this property (pool, air conditioning, laundry on-site, etc.). The features themselves are defined in yet another table labeled Feature.

Property
    pid - primary key
    other property details

Feature
    fid - primary key
    name
    value

Property_Feature
    id - primary key
    pid - foreign key (Property)
    fid - foreign key (Feature)

Let say someone wants to search for property that has air conditioning, and a pool and laundry on-site. How do you query the Property_Feature table for multiple features for the same property if each row only represents one feature? What would the SQL query look like? Is this possible? Is there a better solution?

Thanks for the help and insight.

Answer 1

In terms of database design, yours is the right way to do it. It’s correctly normalized.

For the query, I would simply use exists, like this:

select * from Property
where 
exists (select * from Property_Feature where pid = property.pid and fid = 'key_air_conditioning')
and
exists (select * from Property_Feature where pid = property.pid and fid = 'key_pool')

Where key_air_conditioning and key_pool are obviously the keys for those features.

The performance will be OK even for large databases.