ACID properties in MySQL - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to start a transaction in MySQL.

MySQL

START [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.

Using SAVEPOINT to start a transaction.

In MySQL, to begin a transaction, you use START TRANSACTION.

2fill in blank

medium

Complete the code to save changes permanently in a transaction.

MySQL

[1];

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

AROLLBACK

BSTART TRANSACTION

CSAVEPOINT

DCOMMIT

Attempts:

3 left

💡 Hint

Common Mistakes

Using ROLLBACK instead of COMMIT.

Trying to use START TRANSACTION to save changes.

Use COMMIT to save all changes made in the current transaction permanently.

3fill in blank

hard

Fix the error in the code to undo changes in a transaction.

MySQL

[1];

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

ACOMMIT

BROLLBACK

CSTART TRANSACTION

DSAVEPOINT

Attempts:

3 left

💡 Hint

Common Mistakes

Using COMMIT to undo changes.

Using SAVEPOINT instead of ROLLBACK.

To undo changes made in a transaction, use ROLLBACK.

4fill in blank

hard

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

MySQL

SAVEPOINT [1];
ROLLBACK TO [2];

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

Asp1

Bsp2

Csave1

Dsave2

Attempts:

3 left

💡 Hint

Common Mistakes

Using different names for savepoint and rollback.

Using reserved words as savepoint names.

You name the savepoint and rollback to the same name to undo changes after that point.

5fill in blank

hard

Fill the two blanks to demonstrate atomicity by starting a transaction, inserting a row, and committing.

MySQL

START [1];
INSERT INTO users (name) VALUES ('Alice');
[2];

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

ATRANSACTION

BSAVEPOINT

CROLLBACK

DCOMMIT

Attempts:

3 left

💡 Hint

Common Mistakes

Using ROLLBACK instead of COMMIT.

Not starting the transaction before insert.

Start the transaction and commit to make the INSERT permanent. This demonstrates atomicity: either all changes succeed or none do.

Practice

1. Which of the following is NOT one of the ACID properties in databases?

easy

A. Durability and Speed

B. Consistency

C. Isolation

D. Atomicity

Solution

1. Step 1: Recall the ACID properties

   ACID stands for Atomicity, Consistency, Isolation, and Durability.

2. Step 2: Identify the incorrect option

   Durability and Speed adds "Speed" which is not part of ACID properties.

3. Final Answer:

   Durability and Speed -> Option A

4. Quick Check:

   ACID excludes Speed [OK]

Hint: Remember ACID = Atomicity, Consistency, Isolation, Durability [OK]

Common Mistakes:

• Confusing performance terms with ACID properties
• Thinking Speed is part of ACID
• Mixing up Isolation with Integrity

2. Which SQL statement correctly starts a transaction in MySQL?

easy

A. BEGIN TRANSACTION;

B. START TRANSACTION;

C. OPEN TRANSACTION;

D. INIT TRANSACTION;

Solution

1. Step 1: Recall MySQL transaction syntax

   MySQL uses START TRANSACTION; to begin a transaction.

2. Step 2: Check other options

   Options A, B, and D are not valid MySQL commands for starting transactions.

3. Final Answer:

   START TRANSACTION; -> Option B

4. Quick Check:

   MySQL uses START TRANSACTION [OK]

Hint: Use START TRANSACTION to begin in MySQL [OK]

Common Mistakes:

• Using BEGIN TRANSACTION which is not valid in MySQL
• Confusing with other SQL dialects
• Typing incorrect keywords like OPEN or INIT

3. Consider this sequence in MySQL:

START TRANSACTION;
UPDATE accounts SET balance = balance - 100 WHERE id = 1;
UPDATE accounts SET balance = balance + 100 WHERE id = 2;
COMMIT;

What ACID property does this sequence mainly demonstrate?

medium

A. Consistency - data types are checked

B. Isolation - changes are visible immediately

C. Durability - changes are temporary

D. Atomicity - all changes happen or none

Solution

1. Step 1: Understand the transaction sequence

   The two updates are grouped inside a transaction with COMMIT at the end.

2. Step 2: Identify the ACID property

   Atomicity ensures either both updates happen or none do, preventing partial changes.

3. Final Answer:

   Atomicity - all changes happen or none -> Option D

4. Quick Check:

   Transaction groups changes atomically [OK]

Hint: Atomicity means all or nothing in transactions [OK]

Common Mistakes:

• Confusing Isolation with Atomicity
• Thinking Durability means temporary changes
• Assuming Consistency only checks data types

4. You wrote this MySQL transaction:

START TRANSACTION;
UPDATE inventory SET quantity = quantity - 5 WHERE product_id = 10;
COMMIT;

But sometimes the quantity becomes negative. What ACID property is likely violated?

medium

A. Consistency

B. Isolation

C. Durability

D. Atomicity

Solution

1. Step 1: Analyze the problem

   Quantity becoming negative means data rules are broken.

2. Step 2: Identify violated ACID property

   Consistency ensures data stays valid and follows rules; here it is violated.

3. Final Answer:

   Consistency -> Option A

4. Quick Check:

   Consistency keeps data valid [OK]

Hint: Consistency means data must follow rules always [OK]

Common Mistakes:

• Thinking Atomicity prevents negative values
• Confusing Isolation with data validity
• Assuming Durability fixes data rules

5. In a multi-user MySQL environment, two transactions run:

Transaction 1:
START TRANSACTION;
UPDATE accounts SET balance = balance - 50 WHERE id = 1;
-- waits before COMMIT

Transaction 2:
START TRANSACTION;
SELECT balance FROM accounts WHERE id = 1;
COMMIT;

Which ACID property ensures Transaction 2 does not see the uncommitted balance change from Transaction 1?

hard

A. Atomicity

B. Durability

C. Isolation

D. Consistency

Solution

1. Step 1: Understand concurrent transactions

   Transaction 1 updates but delays commit; Transaction 2 reads the same data.

2. Step 2: Identify ACID property controlling visibility

   Isolation ensures uncommitted changes are hidden from other transactions.

3. Final Answer:

   Isolation -> Option C

4. Quick Check:

   Isolation hides uncommitted changes [OK]

Hint: Isolation hides uncommitted changes from others [OK]

Common Mistakes:

• Confusing Isolation with Atomicity
• Thinking Durability controls visibility
• Assuming Consistency hides uncommitted data