Transactions · Beginner – Online Test

Question 1 ACID Beginner Practice

A money transfer debits one account and then the server crashes before crediting the other. Which ACID property guarantees the debit is undone?

Atomicity Isolation Durability Consistency

Question 2 ACID Beginner Practice

What does the C in ACID promise?

A transaction takes the database from one valid state to another, respecting all constraints and rules Every read returns the latest committed value on every replica Transactions run one at a time Data is copied to several disks

Question 3 ACID Beginner Practice

Which ACID property ensures concurrent transactions do not see each other's intermediate, uncommitted work?

Atomicity Durability Consistency Isolation

Question 4 ACID Beginner Practice

A bank confirms a deposit, then the power fails. After restart the deposit is still there. Which property is this?

Atomicity Consistency Isolation Durability

Question 5 ROLLBACK Beginner Practice Query executed

What is Asha's balance afterwards?

accounts

id	holder	balance
1	Asha	1000
2	Ravi	500

START TRANSACTION;
UPDATE accounts SET balance = balance - 200 WHERE id = 1;
ROLLBACK;
SELECT balance FROM accounts WHERE id = 1;

balance
0

balance
800

balance
1000

balance
1200

Question 6 COMMIT Beginner Practice Query executed

What are the balances after this transfer?

accounts

id	holder	balance
1	Asha	1000
2	Ravi	500

START TRANSACTION;
UPDATE accounts SET balance = balance - 200 WHERE id = 1;
UPDATE accounts SET balance = balance + 200 WHERE id = 2;
COMMIT;
SELECT id, balance FROM accounts ORDER BY id;

id	balance
1	1000
2	500

id	balance
1	800
2	700

id	balance
1	800
2	500

id	balance
1	1200
2	300

Question 7 COMMIT Beginner Practice

What does COMMIT do?

Locks the whole table Undoes the transaction Saves a checkpoint you can roll back to Ends the transaction and makes all its changes permanent and visible to others

Question 8 Basics Beginner Practice

What is a transaction in a DBMS?

A stored procedure A backup of the database Any single SELECT statement A sequence of operations treated as one logical unit of work that either fully completes or has no effect

Question 9 Autocommit Beginner Practice Query executed

No transaction was started. What is Ravi's balance after the ROLLBACK?

accounts

id	holder	balance
1	Asha	1000
2	Ravi	500

UPDATE accounts SET balance = 0 WHERE id = 2;
ROLLBACK;
SELECT balance FROM accounts WHERE id = 2;

balance
0

balance
NULL

balance
(no rows)

balance
500

Question 10 Transaction states Beginner Practice

A transaction has executed its last statement but its changes are not yet safely written. Which state is it in?

Failed Committed Aborted Partially committed

Question 11 Read anomalies Beginner Practice

T1 updates a row; T2 reads the new value; then T1 rolls back. What did T2 experience?

A deadlock A phantom read A non-repeatable read A dirty read – it read data that was never committed

Question 12 Isolation levels Beginner Practice

What is the default isolation level of InnoDB in MySQL and MariaDB?

REPEATABLE READ READ UNCOMMITTED READ COMMITTED SERIALIZABLE

Question 13 Deadlock Beginner Practice

T1 holds a lock on row A and waits for row B; T2 holds row B and waits for row A. What is this?

A cascading rollback A dirty read Starvation A deadlock

Question 14 Consistency Beginner Practice Query executed

balance has CHECK (balance >= 0). Why does the transfer fail?

accounts

id	holder	balance
1	Asha	1000
2	Ravi	500

START TRANSACTION;
UPDATE accounts SET balance = balance - 600 WHERE id = 2;

Ravi's row is locked by another session Ravi has only 500, so the update would make his balance negative and the CHECK rejects it START TRANSACTION needs a name Updates are not allowed inside a transaction

Question 15 ROLLBACK Beginner Practice

Which command discards all changes of the current transaction?

COMMIT DELETE TRUNCATE ROLLBACK

Transactions · Beginner

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