Which of the following Cannot be used to implement a timestamp?

Explanation: An external time counter cannot be used to implement a timestamp. System clock and a logical counter can be used.

What are the types of transaction?

Can triggers be enabled or disabled?

Triggers can be re-enabled by using ENABLE TRIGGER. DML triggers defined on tables can be also be disabled or enabled by using ALTER TABLE. Changing the trigger by using the ALTER TRIGGER statement enables the trigger.

For what purpose are views used?

Views can join and simplify multiple tables into a single virtual table. Views can act as aggregated tables, where the database engine aggregates data (sum, average, etc.) and presents the calculated results as part of the data. Views can hide the complexity of data.

How many times trigger statement executed?

3 Answers. It all depends on the type of trigger you are using. a statement level trigger will fire once for the whole statement.

How is concurrency performed?

It uses system time to determine the time stamp of the transaction. This is the most commonly used concurrency protocol. Lock-based protocols help you to manage the order between the conflicting transactions when they will execute. Timestamp-based protocols manage conflicts as soon as an operation is created.

What are phantom reads?

A Phantom read occurs when one user is repeating a read operation on the same records, but has new records in the results set: READ UNCOMMITTED. Also called a Dirty read. When this isolation level is used, a transaction can read uncommitted data that later may be rolled back.

How do I stop cascading rollback?

What is dirty write in database?

A Dirty Write occurs when one transaction overwrites a value that has previously been written by another still in-flight transaction. One reason why Dirty Writes are bad is that they can violate database consistency.

What is dirty read and phantom read?

Dirty Reads A dirty read occurs when a transaction reads data that has not yet been committed. For example, suppose transaction 1 updates a row. Transaction 2 reads the updated row before transaction 1 commits the update. ... Phantoms A phantom is a row that matches the search criteria but is not initially seen.

What is SQL durability?

In database systems, durability is the ACID property which guarantees that transactions that have committed will survive permanently. For example, if a flight booking reports that a seat has successfully been booked, then the seat will remain booked even if the system crashes.

Why do we use views instead of tables?

Views can provide many advantages over tables:

Views can limit the degree of exposure of the underlying tables to the outer world: a given user may have permission to query the view, while denied access to the rest of the base table. Views can join and simplify multiple tables into a single virtual table.

What is virtual table in SQL?

A virtual table is an object that presents an SQL table interface but which is not stored in the database file, at least not directly. The virtual table mechanism is a feature of SQLite that allows SQLite to access and manipulate resources other than bits in the database file using the powerful SQL query language.

What is the syntax for unique indexes?

The syntax to create an index in SQL is: CREATE [UNIQUE] INDEX index_name ON table_name (column1, column2, ... column_n); UNIQUE.

Are views stored in memory?

The view is a query stored in the data dictionary, on which the user can query just like they do on tables. It does not use the physical memory, only the query is stored in the data dictionary. It is computed dynamically, whenever the user performs any query on it.

What is the syntax for disabling a trigger?

You can subsequently disable the trigger with the following statement: ALTER TRIGGER update_job_history DISABLE; When the trigger is disabled, the database does not fire the trigger when an UPDATE statement changes an employee's job.

What is it called if an object has its own lifecycle and there is no owner?

Explanation: Abstraction is the concept of defining real world objects in terms of classes or interfaces. ... Explanation: It is a relationship where all objects have their own lifecycle and there is no owner. This occurs where many to many relationships are available, instead of one to one or one to many.

What are the four most common types of transactions?

There are four main types of financial transactions that occur in a business. These four types of financial transactions are sales, purchases, receipts, and payments.

What are the 3 main types of bank transactions?

Answer: The three main types of banking are checks, withdrawals, and deposits.

What is accounting cycle?

The accounting cycle is a collective process of identifying, analyzing, and recording the accounting events of a company. It is a standard 8-step process that begins when a transaction occurs and ends with its inclusion in the financial statements.