Database Management DBAS32100

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Questions and Answers

What type of read is prevented under the Read Committed isolation level?

Dirty reads (correct)

Non-repeatable reads

Phantom reads

All types of reads

Which isolation level ensures that Transaction A sees the same balance during its whole transaction, regardless of Transaction B's modifications?

Read Committed

Read Uncommitted

Repeatable Read (correct)

Serializable

What additional guarantees does the Serializable isolation level provide compared to Repeatable Read?

Prevents phantom reads (correct)

Prevents dirty reads only

Allows non-repeatable reads

Allows dirty reads

In the context of isolation levels, what occurs when a transaction reads data multiple times and gets different results?

Non-repeatable read Signup and view all the answers

What does Transaction A experience under Repeatable Read isolation if Transaction B commits changes during its execution?

Sees consistent data throughout its transaction Signup and view all the answers

What is a phantom read?

Reading newly added rows that were committed after the initial read. Signup and view all the answers

Which isolation level allows for dirty reads?

READ UNCOMMITTED Signup and view all the answers

What is the main characteristic of the READ COMMITTED isolation level?

It prevents dirty reads but allows non-repeatable reads. Signup and view all the answers

Which scenario illustrates a non-repeatable read?

Transaction A reads a value, then Transaction B updates it before Transaction A reads it again. Signup and view all the answers

Which isolation level provides the highest degree of consistency?

SERIALIZABLE Signup and view all the answers

What potential issue arises from using an isolation level of READ UNCOMMITTED?

Data may be inconsistent due to concurrent transactions. Signup and view all the answers

What is a likely consequence of a transaction executing under the REPEATABLE READ isolation level?

It can read committed data but may experience phantom reads. Signup and view all the answers

Which isolation level prevents both dirty reads and non-repeatable reads?

SERIALIZABLE Signup and view all the answers

What is the primary concern addressed by the Repeatable Read isolation level?

Preventing non-repeatable reads Signup and view all the answers

Which scenario exemplifies the Read Uncommitted isolation level?

A user checking a bank balance before a pending deposit is completed Signup and view all the answers

What does the Serializable isolation level guarantee?

Transactions appear to run in sequential order Signup and view all the answers

In which situation are phantom reads most likely to occur?

When using the Repeatable Read isolation level Signup and view all the answers

What characteristic does the Read Committed isolation level have?

It prevents dirty reads by only allowing committed data to be read Signup and view all the answers

What is a potential issue with the Repeatable Read isolation level?

It may lead to phantom reads Signup and view all the answers

What happens to a read operation under Read Uncommitted if another transaction rolls back its changes?

The read may reflect incorrect data prior to rollback Signup and view all the answers

Which isolation level provides the highest data consistency across transactions?

Serializable Signup and view all the answers

What is meant by atomicity in the context of a transaction?

All components of a transaction must succeed or fail together. Signup and view all the answers

Which statement regarding DDL operations in Oracle is true?

DDL operations commit any outstanding work before executing. Signup and view all the answers

What does consistency ensure in a transaction?

Database state remains valid after the transaction. Signup and view all the answers

Which of the following best describes First Normal Form (1NF)?

Requires atomic values in each column. Signup and view all the answers

Which of the following describes the purpose of third normal form (3NF)?

To ensure no redundancies exist in data. Signup and view all the answers

Which statement is true about data integrity in relational databases?

Constraints and data types help maintain data integrity. Signup and view all the answers

In second normal form (2NF), what is required about non-key attributes?

They must be dependent on the entire primary key. Signup and view all the answers

What does durability guarantee in a transaction?

Once a transaction is committed, it remains permanent. Signup and view all the answers

What happens to Transaction B's data if Transaction A rolls back after updating a product price?

Transaction B ends up with incorrect data. Signup and view all the answers

What characterizes a non-repeatable read in database transactions?

A later read receives a value that has been changed by another transaction. Signup and view all the answers

In which situation would a phantom read occur?

A transaction inserts a new row while another transaction is reading. Signup and view all the answers

What is the effect of a dirty read in a banking scenario?

Transaction A reads an uncommitted update made by Transaction B. Signup and view all the answers

Which example best illustrates the concept of a phantom read?

Counting people in a room that changes while counting. Signup and view all the answers

How does Transaction A experience a non-repeatable read?

By reading data, then experiencing an update from another transaction. Signup and view all the answers

What is likely to occur if Worker A rolls back their changes after Worker B has used them?

Worker B will experience confusion due to incorrect data. Signup and view all the answers

What does it mean if data is termed as 'non-repeatable'?

The data can change between multiple read operations by the same transaction. Signup and view all the answers

What is the purpose of the UPDATE statement in the transaction involving the checking account?

To deduct $500 from the checking account balance Signup and view all the answers

What occurs when a dirty read happens?

A transaction can read uncommitted data from another transaction Signup and view all the answers

Which statement correctly describes the role of the Transaction_History table?

To keep a record of past transactions including details like time and amount Signup and view all the answers

What SQL command is used to create a new bank account entry?

INSERT INTO Bank_Account Signup and view all the answers

What is a primary key in the context of the Bank_Account table?

Account_Number Signup and view all the answers

What SQL operation is performed to ensure the new balance is reflected in the checking account after the transfer?

UPDATE Bank_Account with COMMIT option Signup and view all the answers

If a transaction is reading data that hasn’t been committed yet, what isolation phenomenon is this usually associated with?

Dirty Reads Signup and view all the answers

What happens if a transaction modifies data before it has been committed by another transaction?

The data becomes accessible for dirty reads Signup and view all the answers

What happens to a transaction if a ROLLBACK is executed?

All changes made since the last COMMIT are discarded. Signup and view all the answers

What is the purpose of a SAVE POINT in a transaction?

To serve as a rollback marker within the same transaction. Signup and view all the answers

Which statement about transactions is true?

Transactions are executed as atomic units, either fully completed or fully undone. Signup and view all the answers

Which scenario describes a deadlock situation?

Two processes are simultaneously waiting for each other to release locks. Signup and view all the answers

When would a DELETE or UPDATE statement not affect the database?

If ROLLBACK is called after it has been run. Signup and view all the answers

Why is it necessary to use ORDER BY in a SELECT statement?

To obtain results in a specific order regardless of insertion sequence. Signup and view all the answers

What best represents the atomicity of a transaction?

Either all changes are applied or none at all. Signup and view all the answers

What occurs if a process is blocked and waiting for another process to release a lock?

Both processes are indefinitely stalled until locks are released. Signup and view all the answers

What is a dirty read?

Reading uncommitted data that could be rolled back. Signup and view all the answers

What characterizes a non-repeatable read?

Reading the same row multiple times with different data values. Signup and view all the answers

What scenario exemplifies a phantom read?

Querying accounts and finding a new account added after the initial query. Signup and view all the answers

If Transaction A reads the balance and Transaction B changes it, then Transaction A reads again, this is an example of which type?

Non-repeatable read Signup and view all the answers

What situation leads to dirty reads?

When one transaction updates data and another transaction reads it before it is committed. Signup and view all the answers

Which description accurately defines a phantom read?

The existence of new results emerging after a data insertion while querying. Signup and view all the answers

What impact does a dirty read have on a transaction?

It can lead to incorrect conclusions from reading uncommitted data. Signup and view all the answers

Which situation exemplifies a non-repeatable read?

A transaction reads data before and after another transaction's commit. Signup and view all the answers

What happens when a transaction is set to the READ UNCOMMITTED isolation level?

The transaction may read uncommitted data which might be incorrect. Signup and view all the answers

Which isolation level prevents dirty reads but allows phantom reads to occur?

READ COMMITTED Signup and view all the answers

Which of the following isolation levels provides the highest level of data isolation?

SERIALIZABLE Signup and view all the answers

What situation best describes a phantom read?

Seeing newly added rows after another transaction has committed changes. Signup and view all the answers

What characterizes the REPEATABLE READ isolation level?

Guarantees that committed data remains unchanged during the transaction. Signup and view all the answers

In which scenario is a non-repeatable read most likely to occur?

When a transaction reads data before another transaction commits. Signup and view all the answers

Which isolation level allows for transactions to see the effects of other transactions after they have committed?

READ COMMITTED Signup and view all the answers

Why might the READ UNCOMMITTED isolation level be problematic?

It allows reading of potentially incorrect data before it is finalized. Signup and view all the answers

What does the function ROLLUP produce when aggregating data?

Aggregated values for specified combinations of groups Signup and view all the answers

When would you typically use GROUP SETS?

To group data based on multiple distinct attributes Signup and view all the answers

What is the primary purpose of using the ROLLUP function in SQL?

To generate subtotals for groups within groups Signup and view all the answers

Which statement best describes how ROLLUP grouping works?

It only aggregates data based on the first column specified Signup and view all the answers

How does GROUP BY differ from ROLLUP in terms of data aggregation?

ROLLUP generates more aggregated data than GROUP BY Signup and view all the answers

What is the primary purpose of aggregate functions in SQL?

To perform calculations on a set of values and return a single result Signup and view all the answers

What does the GROUP BY clause accomplish in SQL?

It aggregates data for every unique value in a column or set of columns Signup and view all the answers

In SQL, what does the HAVING clause do?

It selects rows that meet a specific condition after aggregation Signup and view all the answers

What is one of the key features of the CUBE operation in SQL?

It delivers cross-tabulation values for all combinations of columns Signup and view all the answers

When using the GROUP BY clause with multiple columns, what type of outcome can be expected?

It creates groups based on all combinations of the provided column values Signup and view all the answers

What is a limitation encountered when using GROUP BY in SQL?

Cannot perform calculations on a per row basis Signup and view all the answers

In the context of SQL, what is the function of the ROLLUP operation?

It generates subtotals and grand totals across one or more dimensions Signup and view all the answers

When aggregate functions return values, they generally provide what type of output?

A single value summarizing the calculations Signup and view all the answers

What does the GROUPING function indicate about a column in a GROUP BY list?

Whether the column is part of the aggregated result Signup and view all the answers

What is the purpose of the GROUPING_ID function?

To return an integer representing the aggregation level of columns Signup and view all the answers

Which combination of columns will result in a GROUPING_ID value of 1?

Only the first column is not null Signup and view all the answers

When using the GROUP BY clause, which of the following is not a potential way to group data?

By combinations of class, color, and price Signup and view all the answers

What role does the ROLLUP function serve in SQL queries?

To provide subtotals across specified dimensions Signup and view all the answers

In the context of grouping data, what is a primary use of the HAVING clause?

To filter groups based on aggregate conditions Signup and view all the answers

Which of the following correctly describes how to aggregate data for multiple grouping combinations?

Aggregate based on combinations of class, color, and quantity Signup and view all the answers

What happens when both I_Class and I_Color are null in the context of GROUPING_ID?

GROUPING_ID returns 3 Signup and view all the answers

Study Notes