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All questions of Transaction Management for Software Development Exam
Which of the following is a correct statement about the strict two-phase locking (2PL) protocol in DBMS?- a)Read locks are released immediately after a transaction reads a data item.
- b)Write locks are released immediately after a transaction writes a data item.
- c)Deadlocks can still occur even with strict 2PL.
- d)Multiple transactions can hold exclusive locks on the same data item simultaneously.
Correct answer is option 'C'. Can you explain this answer?
Which of the following is a correct statement about the strict two-phase locking (2PL) protocol in DBMS?
a)
Read locks are released immediately after a transaction reads a data item.
b)
Write locks are released immediately after a transaction writes a data item.
c)
Deadlocks can still occur even with strict 2PL.
d)
Multiple transactions can hold exclusive locks on the same data item simultaneously.
|
Abhijeet Basu answered |
Explanation:
Strict two-phase locking (2PL) is a concurrency control protocol used in database management systems (DBMS) to ensure the serializability of transactions. It consists of two phases: the growing phase and the shrinking phase. In the growing phase, transactions acquire locks on the data items they access, and in the shrinking phase, transactions release the locks they acquired.
Deadlocks can still occur even with strict 2PL:
While strict 2PL provides a mechanism to prevent data inconsistencies and ensures serializability, it does not guarantee the prevention of deadlocks. Deadlocks occur when two or more transactions are waiting for each other to release the locks they hold. In strict 2PL, a transaction holds all its locks until it completes, and this can lead to potential deadlocks.
Example:
Consider two transactions T1 and T2, both of which need to acquire locks on two data items, A and B. If T1 acquires a lock on A and T2 acquires a lock on B, and both transactions then attempt to acquire the lock on the other data item, a deadlock occurs. T1 is waiting for T2 to release the lock on B, and T2 is waiting for T1 to release the lock on A. Neither transaction can proceed, resulting in a deadlock situation.
Solution:
To address deadlocks, additional techniques such as deadlock detection and deadlock prevention are employed. Deadlock detection involves periodically checking for the existence of deadlocks and resolving them if found. Deadlock prevention techniques aim to prevent the occurrence of deadlocks altogether.
In conclusion, while strict 2PL provides a mechanism for ensuring the serializability of transactions by acquiring and releasing locks, it does not guarantee the prevention of deadlocks. Deadlocks can still occur in strict 2PL, and additional techniques are required to detect and resolve or prevent deadlocks from happening.
Strict two-phase locking (2PL) is a concurrency control protocol used in database management systems (DBMS) to ensure the serializability of transactions. It consists of two phases: the growing phase and the shrinking phase. In the growing phase, transactions acquire locks on the data items they access, and in the shrinking phase, transactions release the locks they acquired.
Deadlocks can still occur even with strict 2PL:
While strict 2PL provides a mechanism to prevent data inconsistencies and ensures serializability, it does not guarantee the prevention of deadlocks. Deadlocks occur when two or more transactions are waiting for each other to release the locks they hold. In strict 2PL, a transaction holds all its locks until it completes, and this can lead to potential deadlocks.
Example:
Consider two transactions T1 and T2, both of which need to acquire locks on two data items, A and B. If T1 acquires a lock on A and T2 acquires a lock on B, and both transactions then attempt to acquire the lock on the other data item, a deadlock occurs. T1 is waiting for T2 to release the lock on B, and T2 is waiting for T1 to release the lock on A. Neither transaction can proceed, resulting in a deadlock situation.
Solution:
To address deadlocks, additional techniques such as deadlock detection and deadlock prevention are employed. Deadlock detection involves periodically checking for the existence of deadlocks and resolving them if found. Deadlock prevention techniques aim to prevent the occurrence of deadlocks altogether.
In conclusion, while strict 2PL provides a mechanism for ensuring the serializability of transactions by acquiring and releasing locks, it does not guarantee the prevention of deadlocks. Deadlocks can still occur in strict 2PL, and additional techniques are required to detect and resolve or prevent deadlocks from happening.
Which of the following statements best describes a database transaction?- a)A sequence of SQL statements executed on a database
- b)A collection of database tables
- c)A unit of work that must be performed as a whole or not at all
- d)A set of columns in a database table
Correct answer is option 'C'. Can you explain this answer?
Which of the following statements best describes a database transaction?
a)
A sequence of SQL statements executed on a database
b)
A collection of database tables
c)
A unit of work that must be performed as a whole or not at all
d)
A set of columns in a database table
|
Anisha Basu answered |
Database Transaction Explanation:
Transaction in a database refers to a logical unit of work that contains one or more SQL statements. It is a fundamental concept in database management systems that ensures data integrity and consistency.
Key Points:
- Unit of Work: A transaction is a unit of work that must be performed as a whole or not at all. This means that either all the operations within the transaction are successfully completed, or none of them are.
- Atomicity: Transactions follow the principle of atomicity, which ensures that either all the changes made by the transaction are committed to the database, or none of them are. This helps in maintaining data integrity.
- Consistency: Transactions ensure that the database remains in a consistent state before and after the transaction is executed. Any changes made by the transaction should follow the defined rules and constraints of the database.
- Isolation: Transactions should be isolated from other transactions running concurrently. This means that the changes made by one transaction should not be visible to other transactions until the transaction is committed.
- Durability: Once a transaction is committed, the changes made by the transaction should be permanent and survive system failures. This ensures that the data remains consistent even in case of crashes or errors.
Overall, a database transaction is a crucial concept that helps in maintaining data integrity, consistency, and reliability in database systems.
Transaction in a database refers to a logical unit of work that contains one or more SQL statements. It is a fundamental concept in database management systems that ensures data integrity and consistency.
Key Points:
- Unit of Work: A transaction is a unit of work that must be performed as a whole or not at all. This means that either all the operations within the transaction are successfully completed, or none of them are.
- Atomicity: Transactions follow the principle of atomicity, which ensures that either all the changes made by the transaction are committed to the database, or none of them are. This helps in maintaining data integrity.
- Consistency: Transactions ensure that the database remains in a consistent state before and after the transaction is executed. Any changes made by the transaction should follow the defined rules and constraints of the database.
- Isolation: Transactions should be isolated from other transactions running concurrently. This means that the changes made by one transaction should not be visible to other transactions until the transaction is committed.
- Durability: Once a transaction is committed, the changes made by the transaction should be permanent and survive system failures. This ensures that the data remains consistent even in case of crashes or errors.
Overall, a database transaction is a crucial concept that helps in maintaining data integrity, consistency, and reliability in database systems.
Consider the following SQL code:
BEGIN TRANSACTION;
UPDATE Products SET Price = Price * 1.1 WHERE Category = 'Electronics';
SAVEPOINT sp1;
UPDATE Products SET Price = Price * 1.2 WHERE Category = 'Furniture';
ROLLBACK TO sp1;
COMMIT;
What will be the output of this code?- a)No output
- b)The Price values for products in the 'Electronics' category will be updated
- c)The transaction will be rolled back to the SAVEPOINT, and the changes in the 'Furniture' category will be undone
- d)The COMMIT statement will throw an error
Correct answer is option 'C'. Can you explain this answer?
Consider the following SQL code:
BEGIN TRANSACTION;
UPDATE Products SET Price = Price * 1.1 WHERE Category = 'Electronics';
SAVEPOINT sp1;
UPDATE Products SET Price = Price * 1.2 WHERE Category = 'Furniture';
ROLLBACK TO sp1;
COMMIT;
What will be the output of this code?
BEGIN TRANSACTION;
UPDATE Products SET Price = Price * 1.1 WHERE Category = 'Electronics';
SAVEPOINT sp1;
UPDATE Products SET Price = Price * 1.2 WHERE Category = 'Furniture';
ROLLBACK TO sp1;
COMMIT;
What will be the output of this code?
a)
No output
b)
The Price values for products in the 'Electronics' category will be updated
c)
The transaction will be rolled back to the SAVEPOINT, and the changes in the 'Furniture' category will be undone
d)
The COMMIT statement will throw an error
|
Tech Era answered |
The SAVEPOINT sp1 creates a savepoint in the transaction. The second UPDATE statement modifies the Price values in the 'Furniture' category, but the ROLLBACK TO sp1 statement will roll back the transaction to the savepoint, undoing the changes in the 'Furniture' category.
Which of the following is NOT a characteristic of a database transaction?- a)Atomicity
- b)Durability
- c)Consistency
- d)Flexibility
Correct answer is option 'D'. Can you explain this answer?
Which of the following is NOT a characteristic of a database transaction?
a)
Atomicity
b)
Durability
c)
Consistency
d)
Flexibility
|
CodeNation answered |
Flexibility is not a characteristic of a database transaction. The correct characteristics are Atomicity, Consistency, Isolation, and Durability (ACID).
Consider the following SQL code:
BEGIN TRANSACTION;
UPDATE Employees SET Salary = Salary + 500 WHERE Department = 'IT';
COMMIT;
Which of the following ACID properties does this code violate?- a)Atomicity
- b)Consistency
- c)Isolation
- d)Durability
Correct answer is option 'A'. Can you explain this answer?
Consider the following SQL code:
BEGIN TRANSACTION;
UPDATE Employees SET Salary = Salary + 500 WHERE Department = 'IT';
COMMIT;
Which of the following ACID properties does this code violate?
BEGIN TRANSACTION;
UPDATE Employees SET Salary = Salary + 500 WHERE Department = 'IT';
COMMIT;
Which of the following ACID properties does this code violate?
a)
Atomicity
b)
Consistency
c)
Isolation
d)
Durability
|
Hackers World answered |
The code violates the Atomicity property because it performs multiple salary updates within a single transaction. If one update fails, the others will still be committed, leading to an inconsistent state.
What is the purpose of a transaction log in a DBMS?- a)To store backup copies of the database
- b)To record all the changes made to the database during a transaction
- c)To enforce security constraints on the database
- d)To index the database for faster access
Correct answer is option 'B'. Can you explain this answer?
What is the purpose of a transaction log in a DBMS?
a)
To store backup copies of the database
b)
To record all the changes made to the database during a transaction
c)
To enforce security constraints on the database
d)
To index the database for faster access
|
Codebreakers answered |
The transaction log is used to record all the changes made to the database during the execution of a transaction. It provides a way to recover the database in case of failures or rollbacks.
Consider the following transaction code:BEGIN TRANSACTION;
UPDATE customers SET balance = balance - 100 WHERE id = 1;
UPDATE customers SET balance = balance + 100 WHERE id = 2;
COMMIT;
If the initial balance of customer 1 is $500 and customer 2 is $300, what will be the final balance of customer 1 and customer 2 after the transaction is committed?- a)Customer 1: $400, Customer 2: $400
- b)Customer 1: $400, Customer 2: $300
- c)Customer 1: $500, Customer 2: $400
- d)Customer 1: $500, Customer 2: $300
Correct answer is option 'B'. Can you explain this answer?
Consider the following transaction code:
BEGIN TRANSACTION;
UPDATE customers SET balance = balance - 100 WHERE id = 1;
UPDATE customers SET balance = balance + 100 WHERE id = 2;
COMMIT;
If the initial balance of customer 1 is $500 and customer 2 is $300, what will be the final balance of customer 1 and customer 2 after the transaction is committed?
UPDATE customers SET balance = balance - 100 WHERE id = 1;
UPDATE customers SET balance = balance + 100 WHERE id = 2;
COMMIT;
If the initial balance of customer 1 is $500 and customer 2 is $300, what will be the final balance of customer 1 and customer 2 after the transaction is committed?
a)
Customer 1: $400, Customer 2: $400
b)
Customer 1: $400, Customer 2: $300
c)
Customer 1: $500, Customer 2: $400
d)
Customer 1: $500, Customer 2: $300
|
Simar Sharma answered |
The first UPDATE statement reduces the balance of customer 1 by $100, resulting in a balance of $400. The second UPDATE statement tries to increase the balance of customer 2 by $100, but since the initial balance is $300, the update will not take place. Hence, the final balances are $400 and $300, respectively.
Which of the following is NOT an acid property of database transactions?- a)Atomicity
- b)Integrity
- c)Consistency
- d)Durability
Correct answer is option 'B'. Can you explain this answer?
Which of the following is NOT an acid property of database transactions?
a)
Atomicity
b)
Integrity
c)
Consistency
d)
Durability
|
|
CodeNation answered |
Integrity is not an ACID property of database transactions. The correct ACID properties are Atomicity, Consistency, Isolation, and Durability.
Which of the following is NOT a property of a transaction in DBMS?- a)Atomicity
- b)Consistency
- c)Durability
- d)Scalability
Correct answer is option 'D'. Can you explain this answer?
Which of the following is NOT a property of a transaction in DBMS?
a)
Atomicity
b)
Consistency
c)
Durability
d)
Scalability
|
|
Codebreakers answered |
Scalability is not a property of a transaction. The properties of a transaction in DBMS are ACID properties: Atomicity, Consistency, Isolation, and Durability.
Which of the following is a necessary condition for a schedule to be serializable in DBMS?- a)Conflict Serializability
- b)Deadlock Prevention
- c)Starvation Avoidance
- d)Mutual Exclusion
Correct answer is option 'A'. Can you explain this answer?
Which of the following is a necessary condition for a schedule to be serializable in DBMS?
a)
Conflict Serializability
b)
Deadlock Prevention
c)
Starvation Avoidance
d)
Mutual Exclusion
|
Vikram Singh Baghel answered |
Conflict Serializability is a necessary condition for a schedule to be serializable in DBMS. It means that the order of conflicting operations (e.g., read-write or write-write) in the schedule must be the same as in some serial execution.
Consider the following SQL code:
BEGIN TRANSACTION;
SELECT SUM(Quantity) FROM OrderDetails WHERE OrderID = 1;
UPDATE Orders SET TotalQuantity = <result of the previous query> WHERE OrderID = 1;
COMMIT;
Which of the following ACID properties does this code violate?- a)Atomicity
- b)Consistency
- c)Isolation
- d)Durability
Correct answer is option 'B'. Can you explain this answer?
Consider the following SQL code:
BEGIN TRANSACTION;
SELECT SUM(Quantity) FROM OrderDetails WHERE OrderID = 1;
UPDATE Orders SET TotalQuantity = <result of the previous query> WHERE OrderID = 1;
COMMIT;
Which of the following ACID properties does this code violate?
BEGIN TRANSACTION;
SELECT SUM(Quantity) FROM OrderDetails WHERE OrderID = 1;
UPDATE Orders SET TotalQuantity = <result of the previous query> WHERE OrderID = 1;
COMMIT;
Which of the following ACID properties does this code violate?
a)
Atomicity
b)
Consistency
c)
Isolation
d)
Durability
|
Tanuja Mishra answered |
The code violates the Consistency property because it calculates the sum of Quantity from the OrderDetails table and updates the TotalQuantity in the Orders table based on that value. However, if other transactions modify the OrderDetails table before the UPDATE statement, it may result in inconsistent TotalQuantity values.
Consider the following transaction code:BEGIN TRANSACTION;
INSERT INTO orders (customer_id, product_id, quantity) VALUES (1, 100, 5);
INSERT INTO orders (customer_id, product_id, quantity) VALUES (2, 200, 3);
COMMIT;
What will be the outcome of this transaction?- a)Two new orders will be inserted into the "orders" table.
- b)The transaction will be rolled back, and no changes will be made to the database.
- c)An error will occur due to the missing SELECT statement in the transaction.
- d)The transaction will fail to commit due to a primary key constraint violation.
Correct answer is option 'A'. Can you explain this answer?
Consider the following transaction code:
BEGIN TRANSACTION;
INSERT INTO orders (customer_id, product_id, quantity) VALUES (1, 100, 5);
INSERT INTO orders (customer_id, product_id, quantity) VALUES (2, 200, 3);
COMMIT;
What will be the outcome of this transaction?
INSERT INTO orders (customer_id, product_id, quantity) VALUES (1, 100, 5);
INSERT INTO orders (customer_id, product_id, quantity) VALUES (2, 200, 3);
COMMIT;
What will be the outcome of this transaction?
a)
Two new orders will be inserted into the "orders" table.
b)
The transaction will be rolled back, and no changes will be made to the database.
c)
An error will occur due to the missing SELECT statement in the transaction.
d)
The transaction will fail to commit due to a primary key constraint violation.
|
|
CodeNation answered |
The transaction starts by inserting two new orders into the "orders" table. If the INSERT statements execute successfully without violating any constraints, the changes will be committed, and the new orders will be added to the database.
In a database transaction, the rollback operation is used to:- a)Commit the changes made in the transaction
- b)Undo the changes made in the transaction
- c)Freeze the transaction for further processing
- d)Lock the database for exclusive access
Correct answer is option 'B'. Can you explain this answer?
In a database transaction, the rollback operation is used to:
a)
Commit the changes made in the transaction
b)
Undo the changes made in the transaction
c)
Freeze the transaction for further processing
d)
Lock the database for exclusive access
|
|
CodeNation answered |
The rollback operation is used to undo the changes made in the transaction and restore the database to its state before the transaction started.
Consider the following SQL code:
BEGIN TRANSACTION;
UPDATE Products SET Stock = Stock - 10 WHERE ProductID = 1;
SAVEPOINT sp1;
UPDATE Products SET Stock = Stock - 20 WHERE ProductID = 2;
ROLLBACK TO sp1;
COMMIT;
What will be the output of this code?- a)No output
- b)The Stock value for ProductID 1 will be decreased by 10, and the changes for ProductID 2 will be undone
- c)The transaction will be rolled back to the SAVEPOINT, and the changes for both ProductID 1 and ProductID 2 will be undone
- d)The COMMIT statement will throw an error
Correct answer is option 'C'. Can you explain this answer?
Consider the following SQL code:
BEGIN TRANSACTION;
UPDATE Products SET Stock = Stock - 10 WHERE ProductID = 1;
SAVEPOINT sp1;
UPDATE Products SET Stock = Stock - 20 WHERE ProductID = 2;
ROLLBACK TO sp1;
COMMIT;
What will be the output of this code?
BEGIN TRANSACTION;
UPDATE Products SET Stock = Stock - 10 WHERE ProductID = 1;
SAVEPOINT sp1;
UPDATE Products SET Stock = Stock - 20 WHERE ProductID = 2;
ROLLBACK TO sp1;
COMMIT;
What will be the output of this code?
a)
No output
b)
The Stock value for ProductID 1 will be decreased by 10, and the changes for ProductID 2 will be undone
c)
The transaction will be rolled back to the SAVEPOINT, and the changes for both ProductID 1 and ProductID 2 will be undone
d)
The COMMIT statement will throw an error
|
|
Hackers World answered |
The SAVEPOINT sp1 creates a savepoint, and the ROLLBACK TO sp1 statement rolls back the transaction to the savepoint. Therefore, the changes made for both ProductID 1 and ProductID 2 will be undone.
Which of the following is an example of a concurrency control technique used in DBMS to handle conflicts between transactions?- a)Two-Phase Locking (2PL)
- b)Binary Search Tree (BST)
- c)Breadth-First Search (BFS)
- d)QuickSort Algorithm
Correct answer is option 'A'. Can you explain this answer?
Which of the following is an example of a concurrency control technique used in DBMS to handle conflicts between transactions?
a)
Two-Phase Locking (2PL)
b)
Binary Search Tree (BST)
c)
Breadth-First Search (BFS)
d)
QuickSort Algorithm
|
|
Vikram Singh Baghel answered |
Two-Phase Locking (2PL) is a popular concurrency control technique used in DBMS to handle conflicts between transactions. It ensures serializability by acquiring all necessary locks before accessing data and releasing them only after the transaction is complete.
Consider the following SQL code:
BEGIN TRANSACTION;
UPDATE Orders SET Status = 'Shipped' WHERE OrderID = 1;
DELETE FROM OrderDetails WHERE OrderID = 1;
COMMIT;
What will be the output of this code?- a)No output
- b)The Status value for OrderID 1 will be updated to 'Shipped', and the corresponding rows in the OrderDetails table will be deleted
- c)The transaction will be rolled back due to an error
- d)The COMMIT statement will throw an error
Correct answer is option 'A'. Can you explain this answer?
Consider the following SQL code:
BEGIN TRANSACTION;
UPDATE Orders SET Status = 'Shipped' WHERE OrderID = 1;
DELETE FROM OrderDetails WHERE OrderID = 1;
COMMIT;
What will be the output of this code?
BEGIN TRANSACTION;
UPDATE Orders SET Status = 'Shipped' WHERE OrderID = 1;
DELETE FROM OrderDetails WHERE OrderID = 1;
COMMIT;
What will be the output of this code?
a)
No output
b)
The Status value for OrderID 1 will be updated to 'Shipped', and the corresponding rows in the OrderDetails table will be deleted
c)
The transaction will be rolled back due to an error
d)
The COMMIT statement will throw an error
|
Code Nation answered |
The code will update the Status value for OrderID 1 in the Orders table to 'Shipped' and delete the corresponding rows from the OrderDetails table. If there are no errors, there won't be any output.
Consider the following SQL code:
BEGIN TRANSACTION;
INSERT INTO Orders (OrderID, CustomerID, OrderDate) VALUES (1, 10, '2023-05-15');
INSERT INTO OrderDetails (OrderID, ProductID, Quantity) VALUES (1, 100, 5);
COMMIT;
What will be the output of this code?- a)No output
- b)Two rows will be inserted into the Orders table and the OrderDetails table
- c)The transaction will be rolled back due to an error
- d)The COMMIT statement will throw an error
Correct answer is option 'B'. Can you explain this answer?
Consider the following SQL code:
BEGIN TRANSACTION;
INSERT INTO Orders (OrderID, CustomerID, OrderDate) VALUES (1, 10, '2023-05-15');
INSERT INTO OrderDetails (OrderID, ProductID, Quantity) VALUES (1, 100, 5);
COMMIT;
What will be the output of this code?
BEGIN TRANSACTION;
INSERT INTO Orders (OrderID, CustomerID, OrderDate) VALUES (1, 10, '2023-05-15');
INSERT INTO OrderDetails (OrderID, ProductID, Quantity) VALUES (1, 100, 5);
COMMIT;
What will be the output of this code?
a)
No output
b)
Two rows will be inserted into the Orders table and the OrderDetails table
c)
The transaction will be rolled back due to an error
d)
The COMMIT statement will throw an error
|
TeamUnknown answered |
The two INSERT statements will insert rows into the Orders and OrderDetails tables, and the COMMIT statement will save the changes permanently.
What is the primary purpose of concurrency control in DBMS?- a)To ensure that all transactions are executed in parallel
- b)To manage access to shared resources and avoid conflicts
- c)To improve the performance of database queries
- d)To enforce referential integrity constraints
Correct answer is option 'B'. Can you explain this answer?
What is the primary purpose of concurrency control in DBMS?
a)
To ensure that all transactions are executed in parallel
b)
To manage access to shared resources and avoid conflicts
c)
To improve the performance of database queries
d)
To enforce referential integrity constraints
|
|
Codebreakers answered |
Concurrency control in DBMS is used to manage access to shared resources (e.g., database tables) and prevent conflicts when multiple transactions are executed concurrently. It ensures that transactions are executed in a way that maintains data consistency.
Consider the following transaction code:BEGIN TRANSACTION;
UPDATE products SET price = price * 1.1 WHERE category = 'Electronics';
COMMIT;
What will be the outcome of this transaction?- a)All products in the 'Electronics' category will have their price increased by 10%.
- b)The transaction will be rolled back, and no changes will be made.
- c)An error will occur due to the missing WHERE clause in the UPDATE statement.
- d)The transaction will fail to commit due to a deadlock.
Correct answer is option 'A'. Can you explain this answer?
Consider the following transaction code:
BEGIN TRANSACTION;
UPDATE products SET price = price * 1.1 WHERE category = 'Electronics';
COMMIT;
What will be the outcome of this transaction?
UPDATE products SET price = price * 1.1 WHERE category = 'Electronics';
COMMIT;
What will be the outcome of this transaction?
a)
All products in the 'Electronics' category will have their price increased by 10%.
b)
The transaction will be rolled back, and no changes will be made.
c)
An error will occur due to the missing WHERE clause in the UPDATE statement.
d)
The transaction will fail to commit due to a deadlock.
|
|
Codebreakers answered |
The UPDATE statement will modify the price of all products in the 'Electronics' category, increasing it by 10%. The transaction is then committed, and the changes are permanently applied to the database.
Which of the following techniques is used to ensure isolation and consistency in DBMS?- a)Multi-Version Concurrency Control (MVCC)
- b)Data Encryption
- c)Network Address Translation (NAT)
- d)Graph Data Model
Correct answer is option 'A'. Can you explain this answer?
Which of the following techniques is used to ensure isolation and consistency in DBMS?
a)
Multi-Version Concurrency Control (MVCC)
b)
Data Encryption
c)
Network Address Translation (NAT)
d)
Graph Data Model
|
|
Vikram Singh Baghel answered |
Multi-Version Concurrency Control (MVCC) is a technique used to ensure isolation and consistency in DBMS. It allows multiple versions of data items to coexist, allowing transactions to read a consistent snapshot of the database without blocking concurrent writes.
Consider the following SQL code:
BEGIN TRANSACTION;
DELETE FROM Customers WHERE CustomerID = 5;
ROLLBACK;
What will be the output of this code?- a)No output
- b)The row with CustomerID 5 will be deleted from the Customers table
- c)The transaction will be rolled back, and the row with CustomerID 5 will not be deleted
- d)The ROLLBACK statement will throw an error
Correct answer is option 'C'. Can you explain this answer?
Consider the following SQL code:
BEGIN TRANSACTION;
DELETE FROM Customers WHERE CustomerID = 5;
ROLLBACK;
What will be the output of this code?
BEGIN TRANSACTION;
DELETE FROM Customers WHERE CustomerID = 5;
ROLLBACK;
What will be the output of this code?
a)
No output
b)
The row with CustomerID 5 will be deleted from the Customers table
c)
The transaction will be rolled back, and the row with CustomerID 5 will not be deleted
d)
The ROLLBACK statement will throw an error
|
|
Tech Era answered |
The DELETE statement will attempt to delete the row with CustomerID 5, but the ROLLBACK statement will undo the changes made in the transaction, so the row will not be deleted.
Consider the following SQL code:
BEGIN TRANSACTION;
INSERT INTO Customers (CustomerID, Name) VALUES (1, 'John');
INSERT INTO Customers (CustomerID, Name) VALUES (1, 'Jane');
COMMIT;
Which of the following ACID properties does this code violate?- a)Atomicity
- b)Consistency
- c)Isolation
- d)Durability
Correct answer is option 'B'. Can you explain this answer?
Consider the following SQL code:
BEGIN TRANSACTION;
INSERT INTO Customers (CustomerID, Name) VALUES (1, 'John');
INSERT INTO Customers (CustomerID, Name) VALUES (1, 'Jane');
COMMIT;
Which of the following ACID properties does this code violate?
BEGIN TRANSACTION;
INSERT INTO Customers (CustomerID, Name) VALUES (1, 'John');
INSERT INTO Customers (CustomerID, Name) VALUES (1, 'Jane');
COMMIT;
Which of the following ACID properties does this code violate?
a)
Atomicity
b)
Consistency
c)
Isolation
d)
Durability
|
|
Hackers World answered |
The code violates the Consistency property because it attempts to insert duplicate values for the CustomerID in the Customers table, which violates the uniqueness constraint. This results in an inconsistent state.
Which of the following isolation levels provides the highest degree of concurrency but may lead to non-repeatable reads?- a)Read Uncommitted
- b)Read Committed
- c)Repeatable Read
- d)Serializable
Correct answer is option 'A'. Can you explain this answer?
Which of the following isolation levels provides the highest degree of concurrency but may lead to non-repeatable reads?
a)
Read Uncommitted
b)
Read Committed
c)
Repeatable Read
d)
Serializable
|
|
Codebreakers answered |
Read Uncommitted isolation level allows uncommitted changes made by other transactions to be visible, which can lead to non-repeatable reads. The other isolation levels (Read Committed, Repeatable Read, Serializable) provide stronger guarantees but may have a lower degree of concurrency.
Consider the following transaction code:BEGIN TRANSACTION;
SELECT COUNT(*) FROM orders;
ROLLBACK;- a)The total number of orders in the database will be displayed.
- b)The transaction will be committed, and the number of orders will be displayed.
- c)The transaction will be rolled back, and no result will be displayed.
- d)An error will occur due to the missing WHERE clause in the SELECT statement.
Correct answer is option 'C'. Can you explain this answer?
Consider the following transaction code:
BEGIN TRANSACTION;
SELECT COUNT(*) FROM orders;
ROLLBACK;
SELECT COUNT(*) FROM orders;
ROLLBACK;
a)
The total number of orders in the database will be displayed.
b)
The transaction will be committed, and the number of orders will be displayed.
c)
The transaction will be rolled back, and no result will be displayed.
d)
An error will occur due to the missing WHERE clause in the SELECT statement.
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Codebreakers answered |
The transaction is rolled back using the ROLLBACK statement. This means that the changes made by the transaction are undone, and the database returns to its previous state. Therefore, no result will be displayed.
Which of the following is a violation of the serializability property in DBMS?- a)Dirty Read
- b)Lost Update
- c)Cascadeless Schedule
- d)Serializable Schedule
Correct answer is option 'B'. Can you explain this answer?
Which of the following is a violation of the serializability property in DBMS?
a)
Dirty Read
b)
Lost Update
c)
Cascadeless Schedule
d)
Serializable Schedule
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Vikram Singh Baghel answered |
Lost Update is a violation of the serializability property in DBMS. It occurs when one transaction overwrites the changes made by another transaction before they are committed, leading to the loss of the intermediate update.
Consider the following SQL code:
BEGIN TRANSACTION;
SELECT * FROM Orders;
UPDATE Orders SET OrderDate = '2023-06-01' WHERE OrderID = 1;
SELECT * FROM Orders;
ROLLBACK;
SELECT * FROM Orders;
What will be the output of this code?- a)No output
- b)Two sets of rows from the Orders table will be displayed, showing the original and updated values
- c)The transaction will be rolled back, and only the original set of rows from the Orders table will be displayed
- d)The ROLLBACK statement will throw an error
Correct answer is option 'B'. Can you explain this answer?
Consider the following SQL code:
BEGIN TRANSACTION;
SELECT * FROM Orders;
UPDATE Orders SET OrderDate = '2023-06-01' WHERE OrderID = 1;
SELECT * FROM Orders;
ROLLBACK;
SELECT * FROM Orders;
What will be the output of this code?
BEGIN TRANSACTION;
SELECT * FROM Orders;
UPDATE Orders SET OrderDate = '2023-06-01' WHERE OrderID = 1;
SELECT * FROM Orders;
ROLLBACK;
SELECT * FROM Orders;
What will be the output of this code?
a)
No output
b)
Two sets of rows from the Orders table will be displayed, showing the original and updated values
c)
The transaction will be rolled back, and only the original set of rows from the Orders table will be displayed
d)
The ROLLBACK statement will throw an error
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Hackers World answered |
The first SELECT statement will display the original set of rows from the Orders table. The UPDATE statement will update the OrderDate for the row with OrderID 1, and the second SELECT statement after the COMMIT will display the updated set of rows. The ROLLBACK statement is not executed, so it doesn't affect the output.
Which of the following isolation levels allows the highest concurrency in database transactions?- a)Serializable
- b)Repeatable Read
- c)Read Committed
- d)Read Uncommitted
Correct answer is option 'D'. Can you explain this answer?
Which of the following isolation levels allows the highest concurrency in database transactions?
a)
Serializable
b)
Repeatable Read
c)
Read Committed
d)
Read Uncommitted
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CodeNation answered |
Read Uncommitted isolation level allows the highest concurrency in database transactions as it allows dirty reads.
Consider the following transaction code:BEGIN TRANSACTION;
SELECT COUNT(*) FROM products WHERE category = 'Clothing';
UPDATE products SET price = price * 0.9 WHERE category = 'Clothing';
COMMIT;- a)The total number of products in the 'Clothing' category will be displayed, and their prices will be reduced by 10%.
- b)The total number of products in the 'Clothing' category will be displayed, and their prices will be reduced by 90%.
- c)The transaction will be rolled back, and no changes will be made to the database.
- d)An error will occur due to the missing WHERE clause in the SELECT statement.
Correct answer is option 'C'. Can you explain this answer?
Consider the following transaction code:
BEGIN TRANSACTION;
SELECT COUNT(*) FROM products WHERE category = 'Clothing';
UPDATE products SET price = price * 0.9 WHERE category = 'Clothing';
COMMIT;
SELECT COUNT(*) FROM products WHERE category = 'Clothing';
UPDATE products SET price = price * 0.9 WHERE category = 'Clothing';
COMMIT;
a)
The total number of products in the 'Clothing' category will be displayed, and their prices will be reduced by 10%.
b)
The total number of products in the 'Clothing' category will be displayed, and their prices will be reduced by 90%.
c)
The transaction will be rolled back, and no changes will be made to the database.
d)
An error will occur due to the missing WHERE clause in the SELECT statement.
|
|
Simar Sharma answered |
The transaction starts with a SELECT statement to count the number of products in the 'Clothing' category. However, without using a transaction isolation level like SERIALIZABLE, the subsequent UPDATE statement may conflict with concurrent transactions and cause the entire transaction to be rolled back.
Which of the following is the correct order of transaction states in DBMS?- a)Active, Partially Committed, Committed, Aborted
- b)Active, Committed, Partially Committed, Aborted
- c)Active, Committed, Aborted, Partially Committed
- d)Partially Committed, Active, Committed, Aborted
Correct answer is option 'B'. Can you explain this answer?
Which of the following is the correct order of transaction states in DBMS?
a)
Active, Partially Committed, Committed, Aborted
b)
Active, Committed, Partially Committed, Aborted
c)
Active, Committed, Aborted, Partially Committed
d)
Partially Committed, Active, Committed, Aborted
|
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CodeNation answered |
The correct order of transaction states in DBMS is Active, Committed, Partially Committed, and Aborted.
Consider the following SQL code:
BEGIN TRANSACTION;
UPDATE Customers SET City = 'New York' WHERE CustomerID = 1;
COMMIT;
What will be the output of this code?- a)No output
- b)The City value for CustomerID 1 will be updated to 'New York'
- c)The transaction will be rolled back due to an error
- d)The COMMIT statement will throw an error
Correct answer is option 'B'. Can you explain this answer?
Consider the following SQL code:
BEGIN TRANSACTION;
UPDATE Customers SET City = 'New York' WHERE CustomerID = 1;
COMMIT;
What will be the output of this code?
BEGIN TRANSACTION;
UPDATE Customers SET City = 'New York' WHERE CustomerID = 1;
COMMIT;
What will be the output of this code?
a)
No output
b)
The City value for CustomerID 1 will be updated to 'New York'
c)
The transaction will be rolled back due to an error
d)
The COMMIT statement will throw an error
|
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TeamUnknown answered |
The UPDATE statement will update the City value for the row with CustomerID 1 to 'New York', and the COMMIT statement will save the changes permanently.
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Database Management System (DBMS)
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