Query to select cards and transactions

Question

I have some trouble with a query definition. My database is about operations in a bank and I want to show the card numbers which were used in transactions at all ATMs.

This is how my tables DDL:

CREATE TABLE Cards(
    card_id INT PRIMARY KEY IDENTITY(1,1),
    number VARCHAR(25),
    CVV CHAR(3),
    bankAccount_id INT REFERENCES BankAccount(account_id)
);
CREATE TABLE Transactions(
    transaction_id INT PRIMARY KEY IDENTITY(1,1),
    ATM_id INT REFERENCES ATM(id),
    card_number INT REFERENCES Cards(card_id),
    sum_money INT,
    transaction_time DATETIME
);

And I tried below query:

SELECT *
FROM Cards C
WHERE C.card_id = ALL (SELECT *
                        FROM Transactions T
                        WHERE T.card_number = C.card_id
                        )

And it doesn't work since I used card_id on both sides. Can somebody help me, please?

Answer 1

You can do something like this:

SELECT T.card_number
FROM Cards AS C 
INNER JOIN Transactions AS T
    ON C.card_id = T.card_number
GROUP BY T.card_number -- Grouping up on Card_Number to get the count of unique ATMs each card was used at in the HAVING clause
HAVING COUNT(DISTINCT ATM_id) = (SELECT COUNT(1) FROM ATM) -- Count of distinct ATMs each card was used at needs to equal the total number of ATMs