Question

I have a table called transactions with a many-to-many relationship to items through the items_transactions table.

I want to do something like this:

SELECT "transactions".* 
  FROM "transactions" 
INNER JOIN "items_transactions" 
        ON "items_transactions".transaction_id = "transactions".id 
INNER JOIN "items" 
        ON "items".id = "items_transactions".item_id 
WHERE (items.id IN (<list of items>))

But this gives me all transactions that have one or more of the items in the list associated with it and I only want it to give me the transactions that are associated with all of those items.

Any help would be appreciated.

Answer 1

You have to expand out your query for all of the items in the list:

SELECT "transactions".* 
FROM "transactions" 
WHERE EXISTS (SELECT 1 FROM "items_transactions"
              INNER JOIN "items" ON "items".id = "items_transactions".item_id 
              WHERE "items_transactions".transaction_id = "transactions".id
              AND "items".id = <first item in list>)
AND   EXISTS (SELECT 1 FROM "items_transactions"
              INNER JOIN "items" ON "items".id = "items_transactions".item_id 
              WHERE "items_transactions".transaction_id = "transactions".id
              AND "items".id = <second item in list>)
...

You might also be able to massage it out using IN and COUNT DISTINCT, I’m not sure which would be faster. Something like (completely untested):

SELECT "transactions".* 
FROM "transactions" 
INNER JOIN (SELECT "items_transactions".transaction_id 
            FROM "items_transactions"
            INNER JOIN "items" ON "items".id = "items_transactions".item_id 
            WHERE "items".id IN (<list of items>)
            GROUP BY "items_transactions".transaction_id
            HAVING COUNT(DISTINCT "items".id) = <count of items in list>) matches ON transactions.transaction_id = matches.transaction_id