ACID properties mental model in SQL - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the SQL statement to start a transaction.

SQL

BEGIN [1];

Drag options to blanks, or click blank then click option'

ATRANSACTION

BCOMMIT

CROLLBACK

DSAVEPOINT

Attempts:

3 left

💡 Hint

Common Mistakes

Using COMMIT or ROLLBACK to start a transaction.

Omitting the TRANSACTION keyword.

The BEGIN TRANSACTION statement starts a new transaction in SQL.

2fill in blank

medium

Complete the SQL statement to save changes permanently.

SQL

[1] TRANSACTION;

Drag options to blanks, or click blank then click option'

ABEGIN

BCOMMIT

CROLLBACK

DSAVEPOINT

Attempts:

3 left

💡 Hint

Common Mistakes

Using BEGIN instead of COMMIT to save changes.

Using ROLLBACK which cancels changes.

The COMMIT TRANSACTION statement saves all changes made during the transaction permanently.

3fill in blank

hard

Fix the error in the SQL statement to undo changes in a transaction.

SQL

ROLLBACK [1];

Drag options to blanks, or click blank then click option'

ACOMMIT

BSAVEPOINT

CTRANSACTION

DBEGIN

Attempts:

3 left

💡 Hint

Common Mistakes

Using ROLLBACK SAVEPOINT instead of ROLLBACK TRANSACTION.

Using COMMIT or BEGIN with ROLLBACK.

The correct syntax to undo changes is ROLLBACK TRANSACTION.

4fill in blank

hard

Fill both blanks to create a savepoint and rollback to it.

SQL

SAVEPOINT [1]; ROLLBACK TO [2];

Drag options to blanks, or click blank then click option'

Asp1

Bsp2

Csave1

Dstart

Attempts:

3 left

💡 Hint

Common Mistakes

Using different names for savepoint and rollback.

Using reserved words as savepoint names.

You create a savepoint named sp1 and rollback to the same savepoint sp1.

5fill in blank

hard

Fill all three blanks to demonstrate atomicity with a transaction.

SQL

BEGIN [1]; UPDATE accounts SET balance = balance - 100 WHERE id = 1; UPDATE accounts SET balance = balance + 100 WHERE id = 2; [2]; [3];

Drag options to blanks, or click blank then click option'

ATRANSACTION

BCOMMIT

CROLLBACK

DSAVEPOINT

Attempts:

3 left

💡 Hint

Common Mistakes

Omitting BEGIN TRANSACTION or COMMIT.

Using SAVEPOINT instead of COMMIT or ROLLBACK here.

This code starts a transaction, updates balances, commits the changes, and includes a rollback option to undo if needed, demonstrating atomicity.

Practice

1. Which ACID property ensures that a transaction is completed fully or not at all, like finishing a whole recipe or not starting it?

easy

A. Isolation

B. Consistency

C. Atomicity

D. Durability

Solution

1. Step 1: Understand Atomicity meaning

   Atomicity means a transaction is all-or-nothing, like a recipe that must be fully done or not started.

2. Step 2: Compare with other properties

   Consistency means data rules are followed, Isolation means transactions don't interfere, Durability means changes are saved permanently.

3. Final Answer:

   Atomicity -> Option C

4. Quick Check:

   All or nothing = Atomicity [OK]

Hint: All or nothing means Atomicity [OK]

Common Mistakes:

• Confusing Consistency with Atomicity
• Thinking Isolation means all-or-nothing
• Mixing Durability with Atomicity

2. Which of the following SQL transaction commands is used to make all changes permanent, supporting the Durability property?

easy

A. ROLLBACK

B. COMMIT

C. SAVEPOINT

D. BEGIN TRANSACTION

Solution

1. Step 1: Identify command for saving changes

   COMMIT saves all changes permanently, ensuring Durability.

2. Step 2: Understand other commands

   ROLLBACK undoes changes, SAVEPOINT marks a point to rollback to, BEGIN TRANSACTION starts a transaction.

3. Final Answer:

   COMMIT -> Option B

4. Quick Check:

   Permanent save = COMMIT [OK]

Hint: COMMIT makes changes permanent [OK]

Common Mistakes:

• Choosing ROLLBACK to save changes
• Confusing SAVEPOINT with COMMIT
• Thinking BEGIN TRANSACTION saves data

3. Consider two transactions running at the same time: Transaction 1 adds 100 to an account balance, Transaction 2 subtracts 50. Which ACID property ensures the final balance is correct as if transactions ran one after another?

medium

A. Isolation

B. Consistency

C. Atomicity

D. Durability

Solution

1. Step 1: Understand concurrent transactions

   When two transactions run together, Isolation ensures they don't interfere and produce correct results.

2. Step 2: Differentiate from other properties

   Atomicity is about all-or-nothing, Consistency is about data rules, Durability is about saving changes permanently.

3. Final Answer:

   Isolation -> Option A

4. Quick Check:

   Transactions separated = Isolation [OK]

Hint: No interference means Isolation [OK]

Common Mistakes:

• Mixing Consistency with Isolation
• Thinking Atomicity handles concurrency
• Confusing Durability with Isolation

4. A developer notices that after a system crash, some committed transactions are lost. Which ACID property is likely violated, and what should be fixed?

medium

A. Atomicity; ensure transactions are all-or-nothing

B. Consistency; fix data validation rules

C. Isolation; improve transaction locking

D. Durability; improve data saving and recovery

Solution

1. Step 1: Identify property related to crash recovery

   Durability ensures committed transactions survive crashes and are saved permanently.

2. Step 2: Match problem to property

   Lost committed transactions after crash means Durability is violated and saving/recovery must be improved.

3. Final Answer:

   Durability; improve data saving and recovery -> Option D

4. Quick Check:

   Crash survival = Durability [OK]

Hint: Lost data after crash means Durability issue [OK]

Common Mistakes:

• Confusing Atomicity with crash recovery
• Thinking Isolation fixes lost data
• Mixing Consistency with durability problems

5. A bank system must ensure that transferring money from one account to another never leaves the database in an incorrect state, even if the system crashes or many users act at once. Which combination of ACID properties best guarantees this?

hard

A. Atomicity, Consistency, and Durability

B. Consistency and Isolation

C. Isolation and Durability

D. Atomicity and Durability

Solution

1. Step 1: Identify properties needed for correctness and crash safety

   Atomicity ensures full transfer or none, Consistency keeps data valid, Durability saves changes permanently.

2. Step 2: Understand why Isolation alone is not enough

   Isolation prevents interference but does not guarantee correctness or crash safety alone.

3. Step 3: Combine properties for full guarantee

   Atomicity + Consistency + Durability together ensure safe, correct, and permanent transfers.

4. Final Answer:

   Atomicity, Consistency, and Durability -> Option A

5. Quick Check:

   Safe + correct + permanent = Atomicity + Consistency + Durability [OK]

Hint: All but Isolation ensure correctness and crash safety [OK]

Common Mistakes:

• Ignoring Consistency in correctness
• Thinking Isolation alone is enough
• Missing Durability for crash safety