Oracle DBA Interview Questions and answers

Question.1  What is Consistent Backup?

Answer:    A Consistent backup is one in which the files being backed up contain all changes upto the same system change number (SCN).

Question.2  What is fractured Block?

Answer:   Because the database continues writing to the file during an online backup, there is the possibility of backing up inconsistent data within a block. For example, assume that either RMAN or an operating system utility reads the block while database writer is in the middle of updating the block. In this case, RMAN or the copy utility could read the old data in the top half of the block and the new data in the bottom top half of the block. The block is a fractured block, meaning that the data in this block is not consistent.

Question.3  What are the steps to performing complete recovery on the whole database?

Answer:  Mount the database  Ensure that all datafiles you want to recover are online

Restore a backup of the whole database or the files you want to recover

Apply online or archived redo logs, or a combination of the two

Question.4  What are the steps to performing complete recovery on a tablespace or datafile?

Answer:  Take the tablespace or datafile to be recovered offline if the database is open

Restore a backup of the datafiles you want to recover

Apply online or archived redo logs, or a combination of the two.

Question.5  What are the components of physical database structure of Oracle database?

Answer:   Oracle database is comprised of three types of files. One or more datafiles, two are more redo log files, and one or more control files.

Question.6    What are the components of logical database structure of Oracle database?

Answer:  There are tablespaces and database’s schema objects.

Question.7  What is a tablespace?

Answer:  A database is divided into Logical Storage Unit called tablespaces. A tablespace is used to grouped related logical structures together.

Question.8  What is SYSTEM tablespace and when is it created?

Answer:  Every Oracle database contains a tablespace named SYSTEM, which is automatically created when the database is created. The SYSTEM tablespace always contains the data dictionary tables for the entire database.

Question.9  Explain the relationship among database, tablespace and data file?

Answer:  Each databases logically divided into one or more tablespaces one or more data files are explicitly created for each tablespace.

Question.10  What is schema?

Answer:  A schema is collection of database objects of a user.

Question.11    What are Schema Objects?

Answer:  Schema objects are the logical structures that directly refer to the database’s data. Schema objects include tables, views, sequences, synonyms, indexes, clusters, database triggers, procedures, functions packages and database links.

Question.12  Can objects of the same schema reside in different tablespaces?

Answer :Yes.

Question.13   What is Oracle table?

Answer:   A table is the basic unit of data storage in an Oracle database. The tables of a database hold all of the user accessible data. Table data is stored in rows and columns.

Question.14  What is an Oracle view?

Answer:  A view is a virtual table. Every view has a query attached to it. (The query is a SELECT statement that identifies the columns and rows of the table(s) the view uses.)

Question.15    What are the advantages of views?

Answer:    Provide an additional level of table security, by restricting access to a predetermined set of rows and columns of a table.

– Hide data complexity.

– Simplify commands for the user.

– Present the data in a different perspective from that of the base table.

– Store complex queries.

Question.16     What is an Oracle sequence?

Answer:  A sequence generates a serial list of unique numbers for numerical columns of a database’s tables.

Question.17    What is a synonym?

Answer:  A synonym is an alias for a table, view, sequence or program unit.

Question.18   What are the types of synonyms?

Answer:   There are two types of synonyms private and public.

Only its owner can access a private synonym.

Any database user can access a public synonym.

Question.19    What are synonyms used for?

Answer:   Mask the real name and owner of an object. – Provide public access to an object – Provide location transparency for tables, views or program units of a remote database. – Simplify the SQL statements for database users.

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