DotNet Programing Concept: Oracle Questions

Oracle Interview Questions & Answers:-

1. What is the command to To see current user name

Sql> show user;

2. How to Change the SQL prompt name

SQL> set sqlprompt “Manimara > “

Manimara >

3. Command Switch to DOS prompt

SQL> host

4. How do I eliminate the duplicate rows in a table ?

SQL> delete from table_name where rowid not in (select max(rowid) from table group by duplicate_values_field_name);

SQL> delete duplicate_values_field_name dv from table_name ta where rowid <(select min(rowid) from table_name tb where ta.dv=tb.dv);

5. How do I display row number with records?

To achive this use rownum pseudocolumn with query, like SQL> SQL> select

rownum, ename from emp;

6. Display the records between two range

select rownum, empno, ename from emp where rowid in

(select rowid from emp where rownum <=&upto

minus

select rowid from emp where rownum<&Start);

Enter value for upto: 10

Enter value for Start: 7

7. I know the nvl function only allows the same data type(ie. number or char or date Nvl(comm, 0)), if commission is null then the text “Not Applicable” want to display, instead of blank space. How do I write the query?

SQL> select nvl(to_char(comm.),'NA') from emp;

Output :

NVL(TO_CHAR(COMM),'NA')

-----------------------

300

500

1400

8. Oracle cursor : Implicit & Explicit cursors

Oracle uses work areas called private SQL areas to create SQL statements.

PL/SQL construct to identify each and every work are used, is called as Cursor.

For SQL queries returning a single row, PL/SQL declares all implicit cursors.

For queries that returning more than one row, the cursor needs to be explicitly declared.

9. Explicit Cursor attributes

There are four cursor attributes used in Oracle

cursor_name%Found, cursor_name%NOTFOUND, cursor_name%ROWCOUNT, cursor_name%ISOPEN

10. Implicit Cursor attributes

Same as explicit cursor but prefixed by the word SQL

SQL%Found, SQL%NOTFOUND, SQL%ROWCOUNT, SQL%ISOPEN

Tips : 1. Here SQL%ISOPEN is false, because oracle automatically closed the implicit cursor after executing SQL statements.

2. All are Boolean attributes.

11. Find out nth highest salary from emp table

SELECT DISTINCT (a.sal) FROM EMP A WHERE &N = (SELECT COUNT (DISTINCT (b.sal)) FROM EMP B WHERE a.sal<=b.sal);

Enter value for n: 2

SAL

---------

3700

12. To view installed Oracle version information

SQL> select banner from v$version;

13. Display the number value in Words

SQL> select sal, (to_char(to_date(sal,'j'), 'jsp'))

from emp;

the output like,

SAL (TO_CHAR(TO_DATE(SAL,'J'),'JSP'))

--------- -----------------------------------------------------

800 eight hundred

1600 one thousand six hundred

1250 one thousand two hundred fifty

If you want to add some text like,

Rs. Three Thousand only.

SQL> select sal "Salary ",

(' Rs. '|| (to_char(to_date(sal,'j'), 'Jsp'))|| ' only.'))

"Sal in Words" from emp

Salary Sal in Words

------- ------------------------------------------------------

800 Rs. Eight Hundred only.

1600 Rs. One Thousand Six Hundred only.

1250 Rs. One Thousand Two Hundred Fifty only.

14. Display Odd/ Even number of records

Odd number of records:

select * from emp where (rowid,1) in (select rowid, mod(rownum,2) from emp);

Even number of records:

select * from emp where (rowid,0) in (select rowid, mod(rownum,2) from emp)

15. Which date function returns number value?

months_between

16. Any three PL/SQL Exceptions?

Too_many_rows, No_Data_Found, Value_Error, Zero_Error, Others

17. What are PL/SQL Cursor Exceptions?

Cursor_Already_Open, Invalid_Cursor

18. Other way to replace query result null value with a text

SQL> Set NULL ‘N/A’

to reset SQL> Set NULL ‘’

19. What are the more common pseudo-columns?

SYSDATE, USER , UID, CURVAL, NEXTVAL, ROWID, ROWNUM

20. What is the output of SIGN function?

1 for positive value,

0 for Zero,

-1 for Negative value.

21. What is the maximum number of triggers, can apply to a single table?

12 triggers.

22) What is a relational database management system?

When answering these types of questions you need to answer them in a very detailed manner because everyone in your group can answer them without any difficulty. There should be difference between your approach and the other candidates. Interview candidate should try to present all the information he has in a very detailed and step by step manner. A professional approach should be present.

23) What do you know about normalization? Explain in detail?

24) Explain the difference between a procedure and a function? What do you understand by those terms?

25) Explain about functional dependency and its relation with table design?

26) Explain the different normalization forms?

Remember how you answer shortens your technical interview you are trying to convince the interviewer that you are a suitable candidate for the job.

27) What is a cursor and what are the steps need to be taken?

If possible while answering this question try to explain him the various steps in an order.

28) What are the various types of queries in Oracle ?

The types of queries are:

· Normal Queries

· Sub Queries

· Co-related queries

· Nested queries

· Compound queries

29) What are the components of physical database structure of Oracle database?
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.

30) What are actual and formal parameters ?
Actual Parameters : Subprograms pass information using parameters.The variables or expressions referenced in the parameter list of a subprogram call are actual parameters.For example, the following procedure call lists two actual parameters named emp_num and amount:
Eg.raise_salary(emp_num, amount);
Formal Parameters : The variables declared in a subprogram specification and referenced in the subprogram body are formal parameters.For example, the following procedure declares two formal parameters named emp_id and increase:
Eg.PROCEDURE raise_salary (emp_id INTEGER, increase REAL) IS current_salary REAL;

31) What are various types of joins in Oracle ?
Types of joins are:

· Equijoins

· Non-equijoins

· self join

· outer join

31) What are the components of logical database structure of Oracle database?
There are tablespaces and database’s schema objects.

32) What’s the length of SQL integer?
32 bit

33) What is a tablespace?
A database is divided into Logical Storage Unit called tablespaces. A tablespace is used to grouped related logical structures together.

34)          What is an oracle instance?
35)          What is an Archiver in Oracle?
36)          What is a partition of table in Oracle?

37) What is a transaction in Oracle ?
A transaction is a set of SQL statements between any two COMMIT and ROLLBACK statements.

38) What is SYSTEM tablespace and when is it created?
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.

39) Explain the relationship among database, tablespace and data file ?
Each databases logically divided into one or more tablespaces one or more data files are explicitly created for each tablespace.

40) What are the various types of Exceptions in Oracle ?
User defined Exceptions
Predefined Exceptions

41) What is implicit cursor and how is it used by Oracle ?
An implicit cursor is a cursor which is internally created by Oracle.It is created by Oracle for each individual SQL

42) What is schema?
A schema is collection of database objects of a user.

43) What are the types of Notation in Oracle ?
Position, Named, Mixed and Restrictions.

44)          What is an exception in Oracle?
45)          What is a synonym in Oracle?
46)          What is a join, and what are the different types of joins in Oracle?

47) What are Schema Objects?
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.

48) Can objects of the same schema reside in different tablespaces?
Yes.

49) Can a tablespace hold objects from different schemes?
Yes.

50) What is Oracle table?
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.

51) What is an Oracle view?
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.)

52) What is Partial Backup ?
A Partial Backup is any operating system backup short of a full backup, taken while the database is open or shut down.

53) What is Mirrored on-line Redo Log ?

A mirrored on-line redo log consists of copies of on-line redo log files physically located on separate disks, changes made to one member of the group are made to all members.

54) What are the various types of parameter modes in a procedure in Oracle ?

· IN

· OUT

· INOUT

55) What is Full Backup ?
A full backup is an operating system backup of all data files, on-line redo log files and control file that constitute ORACLE database and the parameter.

56) Can a View based on another View ?
Yes.

57) 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.

58) ODBC stands for?
59) What is mean by de-normalization?

60) Do View contain Data ?
Views do not contain or store data.

61) What are the Referential actions supported by FOREIGN KEY integrity constraint ?
UPDATE and DELETE Restrict - A referential integrity rule that disallows the update or deletion of referenced data. DELETE Cascade - When a referenced row is deleted all associated dependent rows are deleted.

62) What are the type of Synonyms?
There are two types of Synonyms Private and Public.

63) What is a Redo Log ?
The set of Redo Log files YSDATE,UID,USER or USERENV SQL functions, or the pseudo columns LEVEL or ROWNUM.

64) What is an Index Segment ?
Each Index has an Index segment that stores all of its data.

65)          What is a cursor?
66)          Advantages of redo log files?
67)          What is referential integrity?

68) What are the different type of Segments ?
Data Segment, Index Segment, Rollback Segment and Temporary Segment.

69) What are Clusters ?
Clusters are groups of one or more tables physically stores together to share common columns and are often used together.

70) What is an Index ?
An Index is an optional structure associated with a table to have direct access to rows, which can be created to increase the performance of data retrieval. Index can be created on one or more columns of a table.

71) What is an Extent ?
An Extent is a specific number of contiguous data blocks, obtained in a single allocation, and

used to store a specific type of information.

72) What is Table ?
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.

73) What are the advantages of views?
- 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.

74) What is an Oracle sequence?
A sequence generates a serial list of unique numbers for numerical columns of a database’s tables.

75) What is a synonym?
A synonym is an alias for a table, view, sequence or program unit.

76) What is a private synonym?
Only its owner can access a private synonym.

77) What is a public synonym?
Any database user can access a public synonym.

78) What are synonyms used for?

- 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.

79) How are the index updates?
Indexes are automatically maintained and used by Oracle. Changes to table data are automatically incorporated into all relevant indexes.

80) Describe the Normalization principles?

81) What is Rollback Segment ?
A Database contains one or more Rollback Segments to temporarily store “undo” information.

82) 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.

83) How to define Data Block size ?
A data block size is specified for each ORACLE database when the database is created. A database users and allocated free database space in ORACLE data blocks. Block size is specified in INIT.ORA file and can’t be changed latter.

84) What does a Control file Contain ?
A Control file records the physical structure of the database. It contains the following information.
Database Name
Names and locations of a database’s files and redolog files.
Time stamp of database creation.

85) What is difference between UNIQUE constraint and PRIMARY KEY constraint ?

A column defined as UNIQUE can contain Nulls while a column defined as PRIMARY KEY can’t contain Nulls.

86) When does a Transaction end ?
When it is committed or Rollbacked.

87) How does one create a new database? (for DBA)
One can create and modify Oracle databases using the Oracle “dbca” (Database Configuration Assistant) utility. The dbca utility is located in the $ORACLE_HOME/bin directory. The Oracle Universal Installer (oui) normally starts it after installing the database server software.
One can also create databases manually using scripts. This option, however, is falling out of fashion, as it is quite involved and error prone

88) What is a database buffer cache in Oracle?

Use the same extent size for all the segments in a given tablespace. Locally Managed tablespaces (available from 8i onwards) with uniform extent sizes virtually eliminates any tablespace fragmentation. Note that the number of extents per segment does not cause any performance issue anymore, unless they run into thousands and thousands where additional I/O may be required to fetch the additional blocks where extent maps of the segment are stored.

89) What does COMMIT do ?
COMMIT makes permanent the changes resulting from all SQL statements in the transaction. The changes made by the SQL statements of a transaction become visible to other user sessions transactions that start only after transaction is committed.

90) Define Transaction ?
A Transaction is a logical unit of work that comprises one or more SQL statements executed by a single user.

91) What is Read-Only Transaction ?
A Read-Only transaction ensures that the results of each query executed in the transaction are

consistant with respect to the same point in time.

92) What is a deadlock ? Explain .
Two processes wating to update the rows of a table which are locked by the other process then deadlock arises. In a database environment this will often happen because of not issuing proper row lock commands. Poor design of front-end application may cause this situation and the performance of server will reduce drastically.These locks will be released automatically when a commit/rollback operation performed or any one of this processes being
killed externally.

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