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Oracle Interview Questions and Answers



What are the different types of segments?
Data segment, index segment, rollback segment and temporary segment.

What is a data segment?
Each non-clustered table has a data segment. All of the table's data is stored in the extents of its data segment. Each cluster has a data segment. The data of every table in the cluster is stored in the cluster's data segment.

What is an index segment?
Each index has an index segment that stores all of its data.

What is rollback segment?
A database contains one or more rollback segments to temporarily store "undo" information.

What are the uses of rollback segment?
To generate read-consistent database information during database recovery and to rollback uncommitted transactions by the users.

What is a temporary segment?
Temporary segments are created by Oracle when a SQL statement needs a temporary work area to complete execution. When the statement finishes execution, the temporary segment extents are released to the system for future use.

What is a datafile?
Every Oracle database has one or more physical data files. A database's data files contain all the database data. The data of logical database structures such as tables and indexes is physically stored in the data files allocated for a database.

What are the characteristics of data files?
A data file can be associated with only one database. Once created a data file can't change size. One or more data files form a logical unit of database storage called a tablespace.

What is a redo log?
The set of redo log files for a database is collectively known as the database redo log.

What is the function of redo log?
The primary function of the redo log is to record all changes made to data.

What is the use of redo log information?
The information in a redo log file is used only to recover the database from a system or media failure prevents database data from being written to a database's data files.

What does a control file contains?
- Database name
- Names and locations of a database's files and redolog files.
- Time stamp of database creation.

What is the use of control file?
When an instance of an Oracle database is started, its control file is used to identify the database and redo log files that must be opened for database operation to proceed. It is also used in database recovery.

Is it possible to split the print reviewer into more than one region?
Yes

Is it possible to center an object horizontally in a repeating frame that has a variable horizontal size?
Yes

For a field in a repeating frame, can the source come from the column which does not exist in the data group which forms the base for the frame?
Yes

Can a field be used in a report without it appearing in any data group?
Yes

The join defined by the default data link is an outer join yes or no?
Yes

Can a formula column referred to columns in higher group?
Yes

Can a formula column be obtained through a select statement?
Yes

Is it possible to insert comments into sql statements return in the data model editor?
Yes

Is it possible to disable the parameter from while running the report?
Yes

When a form is invoked with call_form, Does oracle forms issues a save point?
Yes

Explain the difference between a hot backup and a cold backup and the benefits associated with each.
A hot backup is basically taking a backup of the database while it is still up and running and it must be in archive log mode. A cold backup is taking a backup of the database while it is shut down and does not require being in archive log mode. The benefit of taking a hot backup is that the database is still available for use while the backup is occurring and you can recover the database to any point in time. The benefit of taking a cold backup is that it is typically easier to administer the backup and recovery process. In addition, since you are taking cold backups the database does not require being in archive log mode and thus there will be a slight performance gain as the database is not cutting archive logs to disk.

You have just had to restore from backup and do not have any control files. How would you go about bringing up this database?
I would create a text based backup control file, stipulating where on disk all the data files where and then issue the recover command with the using backup control file clause.

How do you switch from an init.ora file to a spfile?
Issue the create spfile from pfile command.

Explain the difference between a data block, an extent and a segment.
A data block is the smallest unit of logical storage for a database object. As objects grow they take chunks of additional storage that are composed of contiguous data blocks. These groupings of contiguous data blocks are called extents. All the extents that an object takes when grouped together are considered the segment of the database object.

Give two examples of how you might determine the structure of the table DEPT.
Use the describe command or use the dbms_metadata.get_ddl package.

Where would you look for errors from the database engine?
In the alert log.

Compare and contrast TRUNCATE and DELETE for a table.
Both the truncate and delete command have the desired outcome of getting rid of all the rows in a table. The difference between the two is that the truncate command is a DDL operation and just moves the high water mark and produces a now rollback. The delete command, on the other hand, is a DML operation, which will produce a rollback and thus take longer to complete.

Give the reasoning behind using an index.
Faster access to data blocks in a table.

Give the two types of tables involved in producing a star schema and the type of data they hold.
Fact tables and dimension tables. A fact table contains measurements while dimension tables will contain data that will help describe the fact tables.

What type of index should you use on a fact table?
A Bitmap index.

Give two examples of referential integrity constraints.
A primary key and a foreign key.

A table is classified as a parent table and you want to drop and re-create it. How would you do this without affecting the children tables?
Disable the foreign key constraint to the parent, drop the table, re-create the table, enable the foreign key constraint.

Explain the difference between ARCHIVELOG mode and NOARCHIVELOG mode and the benefits and disadvantages to each.
ARCHIVELOG mode is a mode that you can put the database in for creating a backup of all transactions that have occurred in the database so that you can recover to any point in time. NOARCHIVELOG mode is basically the absence of ARCHIVELOG mode and has the disadvantage of not being able to recover to any point in time. NOARCHIVELOG mode does have the advantage of not having to write transactions to an archive log and thus increases the performance of the database slightly.

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