A comprehensive repository of commonly asked Interview Q&A and a collaboration tool for sharing them.Contains questions from most of the possible topics asked in interviews.. This site provides answers to all these most frequently asked interview questions and also answers to these questions!. Most of the interviews conducted by leading IT companies hover around the questions.
visit http://www.cracktheinterview.org/ for comprehensive overview of interview experiences of candidates who attended interviews for various companies.You can also find the sample question papers of various company interviews and written exams
It’s Official: Facebook Passes 500 Million Users
In a blog post, CEO Mark Zuckerberg writes that, “I could have never imagined all of the ways people would use Facebook () when we were getting started 6 years ago. I want to thank you for being part of making Facebook what it is today and for spreading it around the world.”
Zuckerberg has also announced the launch of Facebook Stories, showcasing interesting ways that people have used the social network around the world. News of the feature leaked over the weekend.
Later today, Zuckerberg is expected to make a rare television appearance on ABC’s World News, where he’ll be interviewed by Diane Sawyer. Presumably, the interview will focus on what the 500 million milestone means for the company, but we also expect a number of questions about recent privacy gaffes and other controversial subjects, including the soon to be released movie based on Facebook’s controversial beginnings.
More to come
Oracle Interview Questions and Answers : SQL
1. To see current user name
Sql> show user;
2. Change SQL prompt name
SQL> set sqlprompt “Manimara > “
Manimara >
Manimara >
3. Switch to DOS prompt
SQL> host
4. How do I eliminate the duplicate rows ?
SQL> delete from table_name where rowid not in (select max(rowid) from table group by
duplicate_values_field_name);
or
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);
Example.
Table Emp
Empno Ename
101 Scott
102 Jiyo
103 Millor
104 Jiyo
105 Smith
delete ename from emp a where rowid < ( select min(rowid) from emp b where a.ename = b.ename);
The output like,
Empno Ename
101 Scott
102 Millor
103 Jiyo
104 Smith
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;
Output:
1 Scott
2 Millor
3 Jiyo
4 Smith
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
ROWNUM EMPNO ENAME
--------- --------- ----------
1 7782 CLARK
2 7788 SCOTT
3 7839 KING
4 7844 TURNER
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')
-----------------------
NA
300
500
NA
1400
NA
NA
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);
1
3
5
Even number of records:
select * from emp where (rowid,0) in (select rowid, mod(rownum,2) from emp)
2
4
6
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.
1. Explain the difference between a database administrator and a data administrator.
Database Administrator :- A person (or group of people) responsible for the maintenance and performance of a database and responsible for the planning, implementation, configuration, and administration of relational database management systems.
Data Administrator :- The individual or organization responsible for the specification, acquisition, and maintenance of data management software and the design, validation, and security of files or databases. The DA is in charge of the data dictionary and data model.
2. Explain the difference between an explicit and an implicit lock.
Explicit Lock :- Lock is explicitly requested for a record or table.
Implicit Lock :- Lock is implied but is not acquired
3. What is lock granularity?
There are many locks available for the database system to have like
Intent Shared, Shared, Intent exclusive, exclusive and Shared Intent exclusive.
Locking granularity refers to the size and hence the number of locks used to ensure the consistency of a database during multiple concurrent updates.
4. In general, how should the boundaries of a transaction be defined?
A transaction ensures that one or more operations execute as an atomic unit of work. If one of the operations within a transaction fails, then all of them are rolled-back so that the application is returned to its prior state. The boundaries that define a group of operations done within a single transaction.
5. Explain the meaning of the expression ACID transaction.
ACID means Atomic, Consistency, Isolation, Durability, so when any transaction happen it should be Atomic that is it should either be complete or fully incomplete. There should not be anything like Semi complete. The Database State should remain consistent after the completion of the transaction. If there are more than one Transaction then the transaction should be scheduled in such a fashion that they remain in Isolation of one another.Durability means that Once a transaction commits, its effects will persist even if there are system failures.
6. Explain the necessity of defining processing rights and responsibilities. How are such responsibilities enforced?
One of the reason to define rights is the security in the database system. If any user is allowed to define the data or alter the data then the database would just be of no use and so processing rights and responsibilities are clearly defined in any database system. The resposibilities are enforced using the table space provided by the database system.
7. Describe the advantages and disadvantages of DBMS-provided and application-provided security.
DBMS provided security :- Any database system requires you to login and then process the data depending on the rights given by the DBA to the user who has logged in. The advatage of such a system is securing the data and providing the user and the DBA the secured platform. Any user who logs in cannot do whatever he want but his role can be defined very easily. There is no major disadvantage about the DBMS provided security apart from overhead of storing the rights and priviledges about the users.
Application-provided security :- It is much similar to the DBMS provided security but the only difference is that its the duty of the programmer creating the application to provide all the seurities so that the data is not mishandled.
8. Explain how a database could be recovered via reprocessing. Why is this generally not feasible?
If we reprocess the transaction then the database can be made to come to a state where the database is consistent and so reprocessing the log can recover the database. Reprocessing is not very feasible for a very simple reason that its very costly from time point of view and requires lots of rework and many transaction are even rollback giving more and more rework.
9. Define rollback and roll forward.
Rollback :- Undoing the changes made by a transaction before it commits or to cancel any changes to a database made during the current transaction
RollForward :- Re-doing the changes made by a transaction after it commits or to overwrite the chnaged calue again to ensure consistency
10. Why is it important to write to the log before changing the database values?
The most important objective to write the log before the database is changed is if there is any need to rollback or rollforward any transaction then if the log are not present then the rollback rollforward cannot be done accurately.