Oracle Interview Questions & Answers part 1


Q: – What is "SCN" ?

The System Change Number (SCN) is an important quantifier that the Oracle database uses to keep track of its state at any given point in time.

Q: – What is the role of "Recover Command" ?

The recover command, as you can imagine, is used during a recovery of the database or one of its files or tablespaces after a database failure.To be able to run this command, you need to have the OSOPER or the OSDBA role. You can perform manual or automatic recovery, and in either case, you're responsible for first restoring all the necessary data files so you can recover your database

Q: –What are the "Temporary Tables" ?

Oracle9i allows you to create temporary tables to hold data just for the duration of a session or even a transaction. After the session or the transaction ends, the table is truncated (i.e., the rows are automatically removed). Temporary tables are handy when you are dealing with complex queries or transactions that require transitory row information before inserting or updating a permanent table.

Q: – What is the "log writer"

The job of the log writer (LGWR) process is to transfer the contents of the redo log buffer to disk. Whenever you make a change to a database table in the form of an insert, update, or delete of data, Oracle writes the change to memory buffers first. The log writer process is in charge of the process of transferring these changes to files on disk (the redo log files).

Q: –Which are oracle background processes ?

Database writer
Log writer
Process monitor
System monitor
Coordination job

Q: –What is Transaction Processing in Oracle ?

A transaction is defined as a discrete unit of work in Oracle and consists of at least one SQL statement. The transaction completes when it is completely made permanent or committed, or it is completely undone or rolled back. Note that either the user executing the transaction or a malfunction of the database (e.g., due to inadequate space in a table) can roll back a SQL statement. If the user does the rollback, it is done explicitly using the rollback statement. The user, similarly, performs a commit by using the commit statement.In addition to the commit and rollback statements, users can use the save point statement, which will commit the results of a long transaction until a certain intermediate point only. If a program successfully completes and the user exists gracefully from SQL*Plus, the results are implicitly committed, even without the commit command.

Q: – Is ORACLE database is RDBMS ?


Q: –What is Primary Key ?

A primary key is a field or a combination of fields (columns, to be accurate) that uniquely identifies each record (or row)in a table. It is common to use social security numbers as primary keys because it's obvious that every person has a unique social security number. If there is no appropriate field you can choose as a primary key, you can use system-generated numbers to uniquely identify your rows. A primary key must be unique and present in every row of the table to maintain the validity of the data.

Q: – What environment variables are in force when you first log in?

$ env

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