Question

Imagine you have two tables, with a one to many relationship.

For this example, I will suggest that there are two tables: Person, and Homes.
The person table holds a persons name, and gives them an ID. The homes table, holds the association of homes to a person. PID joins to “Person.ID”

And, in this tiny DB, a person can have no homes, or many homes.

I hope I drew that right.

How do I write a select, that returns everyone with every specified house type?

Let’s say these are valid “Types” in the homes table:

Cottage, Main, Mansion, Spaceport.

I want to return everyone, in the Person table, who has a spaceport and a Cottage.

The best I could come up with was this:

SELECT DISTINCT( p.name ) AS name
FROM person p
    INNER JOIN homes h ON h.pid = p.id
WHERE 'spaceport' in (
    SELECT DISTINCT( type ) AS type
    FROM homes
    WHERE pid = p.id
)
AND 'cottage' in (
    SELECT DISTINCT( type ) AS type
    FROM homes
    WHERE pid = p.id
)

When I wrote that, it works, but I’m pretty sure there has to be a better way.

Answer 1

The HAVING clause here will guarantee that the persons returned have both types, not just one or the other.

SELECT p.name
    FROM person p
        INNER JOIN homes h
            ON p.id = h.pid
                AND h.type IN ('spaceport', 'cottage')
    GROUP BY p.name
    HAVING COUNT(DISTINCT h.type) = 2