Set - 6

Question 1 :

What is Database Trigger ?

Answer :

A Database Trigger is procedure (set of SQL and PL/SQL statements) that is automatically executed as a result of an insert in, update to, or delete from a table.


Question 2 :

Can the default values be assigned to actual parameters?

Answer :

Yes


Question 3 :

Can a primary key contain more than one columns?

Answer :

Yes


Question 4 :

What is an UTL_FILE.What are different procedures and functions associated with it?

Answer :

UTL_FILE is a package that adds the ability to read and write to operating system files. Procedures associated with it are FCLOSE, FCLOSE_ALL and 5 procedures to output data to a file PUT, PUT_LINE, NEW_LINE, PUTF, FFLUSH.PUT, FFLUSH.PUT_LINE,FFLUSH.NEW_LINE. Functions associated with it are FOPEN, ISOPEN.


Question 5 :

What are ORACLE PRECOMPILERS?

Answer :

Using ORACLE PRECOMPILERS, SQL statements and PL/SQL blocks can be contained inside 3GL programs written in C,C++,COBOL,PASCAL, FORTRAN,PL/1 AND ADA. The Precompilers are known as Pro*C,Pro*Cobol,... This form of PL/SQL is known as embedded pl/sql,the language in which pl/sql is embedded is known as the host language. The prcompiler translates the embedded SQL and pl/sql statements into calls to the precompiler runtime library. The output must be compiled and linked with this library to creator an executable.


Question 6 :

Differentiate between TRUNCATE and DELETE?

Answer :

TRUNCATE deletes much faster than DELETE
TRUNCATE
DELETE
It is a DDL statement
It is a DML statement
It is a one way trip, cannot ROLLBACK
One can Rollback
Doesn't have selective features (where clause)
Has
Doesn't fire database triggers
Does
It requires disabling of referential constraints.


Question 7 :

What is difference between a formal and an actual parameter?

Answer :

The variables declared in the procedure and which are passed, as arguments are called actual, the parameters in the procedure declaration. Actual parameters contain the values that are passed to a procedure and receive results. Formal parameters are the placeholders for the values of actual parameters


Question 8 :

What should be the return type for a cursor variable. Can we use a scalar data type as return type?

Answer :

The return type for a cursor must be a record type.It can be declared explicitly as a user-defined or %ROWTYPE can be used. eg TYPE t_studentsref IS REF CURSOR RETURN students%ROWTYPE


Question 9 :

What are different Oracle database objects?

Answer :

-TABLES
-VIEWS
-INDEXES
-SYNONYMS
-SEQUENCES
-TABLESPACES etc


Question 10 :

What is difference between SUBSTR and INSTR?

Answer :

SUBSTR returns a specified portion of a string eg SUBSTR('BCDEF',4) output BCDE INSTR provides character position in which a pattern is found in a string. eg INSTR('ABC-DC-F','-',2) output 7 (2nd occurence of '-')


Question 11 :

Display the number value in Words?

Answer :

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.


Question 12 :

What is difference between SQL and SQL*PLUS?

Answer :

SQL*PLUS is a command line tool where as SQL and PL/SQL language interface and reporting tool. Its a command line tool that allows user to type SQL commands to be executed directly against an Oracle database. SQL is a language used to query the relational database(DML,DCL,DDL). SQL*PLUS commands are used to format query result, Set options, Edit SQL commands and PL/SQL.


Question 13 :

What are various joins used while writing SUBQUERIES?

Answer :

Self join-Its a join foreign key of a table references the same table. Outer Join--Its a join condition used where One can query all the rows of one of the tables in the join condition even though they don't satisfy the join condition.
Equi-join--Its a join condition that retrieves rows from one or more tables in which one or more columns in one table are equal to one or more columns in the second table.


Question 14 :

What a SELECT FOR UPDATE cursor represent.?

Answer :

SELECT......FROM......FOR......UPDATE[OF column-reference][NOWAIT]
The processing done in a fetch loop modifies the rows that have been retrieved by the cursor. A convenient way of modifying the rows is done by a method with two parts: the FOR UPDATE clause in the cursor declaration, WHERE CURRENT OF CLAUSE in an UPDATE or declaration statement.


Question 15 :

What are various privileges that a user can grant to another user?

Answer :

-SELECT
-CONNECT
-RESOURCES


Question 16 :

Display the records between two range?

Answer :

select rownum, empno, ename from emp where rowid in (select rowid from emp where rownum <=&upto minus select rowid from emp where rownum<&Start);


Question 17 :

minvalue.sql Select the Nth lowest value from a table?

Answer :

select level, min('col_name') from my_table where level = '&n' connect by prior ('col_name') < 'col_name')
group by level;
Example:
Given a table called emp with the following columns:
-- id number
-- name varchar2(20)
-- sal number
--
-- For the second lowest salary:
-- select level, min(sal) from emp
-- where level=2
-- connect by prior sal < sal
-- group by level


Question 18 :

What is difference between Rename and Alias?

Answer :

Rename is a permanent name given to a table or column whereas Alias is a temporary name given to a table or column which do not exist once the SQL statement is executed.


Question 19 :

Difference between an implicit & an explicit cursor.?

Answer :

only one row. However,queries that return more than one row you must declare an explicit cursor or use a cursor FOR loop. Explicit cursor is a cursor in which the cursor name is explicitly assigned to a SELECT statement via the CURSOR...IS statement. An implicit cursor is used for all SQL statements Declare, Open, Fetch, Close. An explicit cursors are used to process multirow SELECT statements An implicit cursor is used to process INSERT, UPDATE, DELETE and single row SELECT. .INTO statements.


Question 20 :

What is a OUTER JOIN?

Answer :

Outer Join--Its a join condition used where you can query all the rows of one of the tables in the join condition even though they don't satisfy the join condition.


Question 21 :

What is a cursor?

Answer :

Oracle uses work area to execute SQL statements and store processing information PL/SQL construct called a cursor lets you name a work area and access its stored information A cursor is a mechanism used to fetch more than one row in a Pl/SQl block.


Question 22 :

What is the purpose of a cluster?

Answer :

Oracle does not allow a user to specifically locate tables, since that is a part of the function of the RDBMS. However, for the purpose of increasing performance, oracle allows a developer to create a CLUSTER. A CLUSTER provides a means for storing data from different tables together for faster retrieval than if the table placement were left to the RDBMS.
What is OCI. What are its uses?
Oracle Call Interface is a method of accesing database from a 3GL program. Uses--No precompiler is required,PL/SQL blocks are executed like other DML statements.
The OCI library provides
--functions to parse SQL statemets
--bind input variables
--bind output variables
--execute statements
--fetch the results


Question 23 :

How you open and close a cursor variable. Why it is required?

Answer :

OPEN cursor variable FOR SELECT...Statement
CLOSE cursor variable In order to associate a cursor variable with a particular SELECT statement OPEN syntax is used. In order to free the resources used for the query CLOSE statement is used.
Display Odd/ Even number of records?
Odd number of records:
select * from emp where (rowid,1) in (select rowid, mod(rownum,2) from emp);
Output:-
1
3
5
Even number of records:
select * from emp where (rowid,0) in (select rowid, mod(rownum,2) from emp)
Output:-
2
4
6


Question 24 :

What are various constraints used in SQL?

Answer :

-NULL
-NOT NULL
-CHECK
-DEFAULT


Question 25 :

Can cursor variables be stored in PL/SQL tables. If yes how. If not why?

Answer :

No, a cursor variable points a row which cannot be stored in a two-dimensional PL/SQL table.


Question 26 :

Difference between NO DATA FOUND and %NOTFOUND?

Answer :

NO DATA FOUND is an exception raised only for the SELECT....INTO statements when the where clause of the querydoes not match any rows. When the where clause of the explicit cursor does not match any rows the %NOTFOUND attribute is set to TRUE instead.


Question 27 :

Can you use a commit statement within a database trigger?

Answer :

No


Question 28 :

What WHERE CURRENT OF clause does in a cursor?

Answer :

LOOP
SELECT num_credits INTO v_numcredits FROM classes
WHERE dept=123 and course=101;
UPDATE students
FHKO;;;;;;;;;SET current_credits=current_credits+v_numcredits
WHERE CURRENT OF X;


Question 29 :

There is a string 120000 12 0 .125 , how you will find the position of the decimal place?

Answer :

INSTR('120000 12 0 .125',1,'.')
output 13


Question 30 :

What are different modes of parameters used in functions and procedures?

Answer :

-IN -OUT -INOUT


Question 31 :

How you were passing cursor variables in PL/SQL 2.2?

Answer :

In PL/SQL 2.2 cursor variables cannot be declared in a package.This is because the storage for a cursor variable has to be allocated using Pro*C or OCI with version 2.2, the only means of passing a cursor variable to a PL/SQL block is via bind variable or a procedure parameter.


Question 32 :

When do you use WHERE clause and when do you use HAVING clause?

Answer :

HAVING clause is used when you want to specify a condition for a group function and it is written after GROUP BY clause. The WHERE clause is used when you want to specify a condition for columns, single row functions except group functions and it is written before GROUP BY clause if it is used.


Question 33 :

Difference between procedure and function.?

Answer :

Functions are named PL/SQL blocks that return a value and can be called with arguments procedure a named block that can be called with parameter. A procedure all is a PL/SQL statement by itself, while a Function call is called as part of an expression.


Question 34 :

Which is more faster - IN or EXISTS?

Answer :

EXISTS is more faster than IN because EXISTS returns a Boolean value whereas IN returns a value.


Question 35 :

What is syntax for dropping a procedure and a function .Are these operations possible?

Answer :

Drop Procedure procedure_name
Drop Function function_name


Question 36 :

How will you delete duplicating rows from a base table?

Answer :

delete from table_name where rowid not in (select max(rowid) from table group by duplicate_values_field_name); or delete duplicate_values_field_name dv from table_name ta where rowid <(select min(rowid) from table_name tb where ta.dv=tb.dv);


Question 37 :

Difference between database triggers and form triggers?

Answer :

-Data base trigger(DBT) fires when a DML operation is performed on a data base table. Form trigger(FT) Fires when user presses a key or navigates between fields on the screen
-Can be row level or statement level No distinction between row level and statement level.
-Can manipulate data stored in Oracle tables via SQL Can manipulate data in Oracle tables as well as variables in forms.
-Can be fired from any session executing the triggering DML statements. Can be fired only from the form that define the trigger.
-Can cause other database triggers to fire. Can cause other database triggers to fire, but not other form triggers.


Question 38 :

What is a cursor for loop?

Answer :

Cursor For Loop is a loop where oracle implicitly declares a loop variable, the loop index that of the same record type as the cursor's record.


Question 39 :

How you will avoid duplicating records in a query?

Answer :

By using DISTINCT


Question 40 :

What is a view ?

Answer :

A view is stored procedure based on one or more tables, it's a virtual table.


Question 41 :

What is difference between UNIQUE and PRIMARY KEY constraints?

Answer :

A table can have only one PRIMARY KEY whereas there can be any number of UNIQUE keys. The columns that compose PK are automatically define NOT NULL, whereas a column that compose a UNIQUE is not automatically defined to be mandatory must also specify the column is NOT NULL.


Question 42 :

What is use of a cursor variable? How it is defined?

Answer :

A cursor variable is associated with different statements at run time, which can hold different values at run time. Static cursors can only be associated with one run time query. A cursor variable is reference type (like a pointer in C).
Declaring a cursor variable:
TYPE type_name IS REF CURSOR RETURN return_type type_name is the name of the reference type,return_type is a record type indicating the types of the select list that will eventually be returned by the cursor variable.


Question 43 :

How do you find the numbert of rows in a Table ?

Answer :

A bad answer is count them (SELECT COUNT(*) FROM table_name)
A good answer is :-
'By generating SQL to ANALYZE TABLE table_name COUNT STATISTICS by querying Oracle System Catalogues (e.g. USER_TABLES or ALL_TABLES).
The best answer is to refer to the utility which Oracle released which makes it unnecessary to do ANALYZE TABLE for each Table individually.


Question 44 :

What is the maximum buffer size that can be specified using the DBMS_OUTPUT.ENABLE function?

Answer :

1,000,00


Question 45 :

What are cursor attributes?

Answer :

-%ROWCOUNT
-%NOTFOUND
-%FOUND
-%ISOPEN


Question 46 :

There is a % sign in one field of a column. What will be the query to find it?

Answer :

'' Should be used before '%'.


Question 47 :

What is ON DELETE CASCADE ?

Answer :

When ON DELETE CASCADE is specified ORACLE maintains referential integrity by automatically removing dependent foreign key values if a referenced primary or unique key value is removed.


Question 48 :

What is the fastest way of accessing a row in a table ?

Answer :

Using ROWID.CONSTRAINTS


Question 49 :

What is difference between TRUNCATE & DELETE ?

Answer :

TRUNCATE commits after deleting entire table i.e., can not be rolled back. Database triggers do not fire on TRUNCATEDELETE allows the filtered deletion. Deleted records can be rolled back or committed. Database triggers fire on DELETE.


Question 50 :

What is a transaction ?

Answer :

Transaction is logical unit between two commits and commit and rollback.


Question 51 :

What are the advantages of VIEW ?

Answer :

To protect some of the columns of a table from other users.To hide complexity of a query.To hide complexity of calculations.


Question 52 :

How will you a activate/deactivate integrity constraints ?

Answer :

The integrity constraints can be enabled or disabled by ALTER TABLE ENABLE constraint/DISABLE constraint.


Question 53 :

Where the integrity constraints are stored in Data Dictionary ?

Answer :

The integrity constraints are stored in USER_CONSTRAINTS.


Question 54 :

What is the Subquery ?

Answer :

Sub query is a query whose return values are used in filtering conditions of the main query.


Question 55 :

How to access the current value and next value from a sequence ? Is it possible to access the current value in a session before accessing next value ?

Answer :

Sequence name CURRVAL, Sequence name NEXTVAL.It is not possible. Only if you access next value in the session, current value can be accessed.


Question 56 :

What are the usage of SAVEPOINTS ?value in a session before accessing next value ?

Answer :

SAVEPOINTS are used to subdivide a transaction into smaller parts. It enables rolling back part of a transaction. Maximum of five save points are allowed.


Question 57 :

What is ROWID ?in a session before accessing next value ?

Answer :

ROWID is a pseudo column attached to each row of a table. It is 18 character long, blockno, rownumber are the components of ROWID.


Question 58 :

Explain Connect by Prior ?in a session before accessing next value ?

Answer :

Retrieves rows in hierarchical order.e.g. select empno, ename from emp where.


Question 59 :

How many LONG columns are allowed in a table ? Is it possible to use LONG columns in WHERE clause or ORDER BY ?

Answer :

Only one LONG columns is allowed. It is not possible to use LONG column in WHERE or ORDER BY clause.


Question 60 :

What is Referential Integrity ?

Answer :

Maintaining data integrity through a set of rules that restrict the values of one or more columns of the tables based on the values of primary key or unique key of the referenced table.


Question 61 :

What is a join ? Explain the different types of joins ?

Answer :

Join is a query which retrieves related columns or rows from multiple tables.Self Join - Joining the table with itself.Equi Join - Joining two tables by equating two common columns.Non-Equi Join - Joining two tables by equating two common columns.Outer Join - Joining two tables in such a way that query can also retrieve rows that do not have corresponding join value in the other table.


Question 62 :

If an unique key constraint on DATE column is created, will it validate the rows that are inserted with SYSDATE ?

Answer :

It won't, Because SYSDATE format contains time attached with it.


Question 63 :

How does one stop and start the OMS? (for DBA)

Answer :

Use the following command sequence to stop and start the OMS (Oracle Management Server):
oemctl start oms
oemctl status oms sysman/oem_temp
oemctl stop oms sysman/oem_temp
Windows NT/2000 users can just stop and start the required services. The default OEM administrator is "sysman" with a password of "oem_temp".
NOTE: Use command oemctrl instead of oemctl for Oracle 8i and below.


Question 64 :

What is an Integrity Constraint ?

Answer :

Integrity constraint is a rule that restricts values to a column in a table.


Question 65 :

How does one create a repository? (for DBA)

Answer :

For OEM v2 and above, start the Oracle Enterprise Manager Configuration Assistant (emca on Unix) to create and configure the management server and repository. Remember to setup a backup for the repository database after creating it.


Question 66 :

If a View on a single base table is manipulated will the changes be reflected on the base table ?

Answer :

If changes are made to the tables which are base tables of a view will the changes be reference on the view.
The following describes means to create a OEM V1.x (very old!!!) repository on WindowsNT:
. Create a tablespace that would hold the repository data. A size between 200- 250 MB would be ideal. Let us call it Dummy_Space.
. Create an Oracle user who would own this repository. Assign DBA, SNMPAgent, Exp_Full_database, Imp_Full_database roles to this user. Lets call this user Dummy_user. Assign Dummy_Space as the default tablespace.
. Create an operating system user with the same name as the Oracle username. I.e. Dummy_User. Add 'Log on as a batch job' under advanced rights in User manager.
. Fire up Enterprise manager and log in as Dummy_User and enter the password. This would trigger the creation of the repository. From now on, Enterprise manager is ready to accept jobs.


Question 67 :

What is a database link ?

Answer :

Database Link is a named path through which a remote database can be accessed.


Question 68 :

How does one list one's databases in the OEM Console? (for DBA)

Answer :

Follow these steps to discover databases and other services from the OEM Console:
1. Ensure the GLOBAL_DBNAME parameter is set for all databases in your LISTENER.ORA file (optional). These names will be listed in the OEM Console. Please note that names entered are case sensitive. A portion of a listener.ora file:
(SID_DESC =
(GLOBAL_DBNAME = DB_name_for_OEM)
(SID_NAME = ...
2. Start the Oracle Intelligent Agent on the machine you want to discover. See section "How does one start the Oracle Intelligent Agent?".
3. Start the OEM Console, navigate to menu "Navigator/ Discover Nodes". The OEM Discovery Wizard will guide you through the process of discovering your databases and other services.


Question 69 :

What is CYCLE/NO CYCLE in a Sequence ?

Answer :

CYCLE specifies that the sequence continues to generate values after reaching either maximum or minimum value. After pan ascending sequence reaches its maximum value, it generates its minimum value. After a descending sequence reaches its minimum, it generates its maximum.NO CYCLE specifies that the sequence cannot generate more values after reaching its maximum or minimum value.


Question 70 :

What is correlated sub-query ?

Answer :

Correlated sub query is a sub query which has reference to the main query.


Question 71 :

What are the data types allowed in a table ?

Answer :

CHAR,VARCHAR2,NUMBER,DATE,RAW,LONG and LONG RAW.


Question 72 :

What is difference between CHAR and VARCHAR2 ? What is the maximum SIZE allowed for each type ?

Answer :

CHAR pads blank spaces to the maximum length. VARCHAR2 does not pad blank spaces. For CHAR it is 255 and 2000 for VARCHAR2.


Question 73 :

Can a view be updated/inserted/deleted? If Yes under what conditions ?

Answer :

A View can be updated/deleted/inserted if it has only one base table if the view is based on columns from one or more tables then insert, update and delete is not possible.


Question 74 :

What are the different types of Coordinations of the Master with the Detail block?

Answer :

POPULATE_GROUP(function)
POPULATE_GROUP_WITH_QUERY(function)
SET_GROUP_CHAR_CELL(procedure)
SET_GROUPCELL(procedure)
SET_GROUP_NUMBER_CELL(procedure)


Question 75 :

Use the ADD_GROUP_COLUMN function to add a column to a record group that was created at design time?
I) TRUE II) FALSE

Answer :

II) FALSE


Question 76 :

Use the ADD_GROUP_ROW procedure to add a row to a static record group?
I) TRUE II) FALSE

Answer :

I) FALSE


Question 77 :

maxvalue.sql Select the Nth Highest value from a table?

Answer :

select level, max('col_name') from my_table where level = '&n' connect by prior ('col_name') > 'col_name')
group by level;
Example:
Given a table called emp with the following columns:
-- id number
-- name varchar2(20)
-- sal number
--
-- For the second highest salary:
-- select level, max(sal) from emp
-- where level=2
-- connect by prior sal > sal
-- group by level


Question 78 :

Find out nth highest salary from emp table?

Answer :

SELECT DISTINCT (a.sal) FROM EMP A WHERE &N = (SELECT COUNT (DISTINCT (b.sal)) FROM EMP B WHERE a.sal<=b.sal);
For E.g.:-
Enter value for n: 2
SAL
---------
3700


Question 79 :

Suppose a customer table is having different columns like customer no, payments.What will be the query to select top three max payments?

Answer :

SELECT customer_no, payments from customer C1
WHERE 3<=(SELECT COUNT(*) from customer C2
WHERE C1.payment <= C2.payment)


Question 80 :

How you will avoid your query from using indexes?

Answer :

SELECT * FROM emp
Where emp_no+' '=12345;
i.e you have to concatenate the column name with space within codes in the where condition.
SELECT /*+ FULL(a) */ ename, emp_no from emp
where emp_no=1234;
i.e using HINTS


Question 81 :

What utility is used to create a physical backup?

Answer :

Either rman or alter tablespace begin backup will do..


Question 82 :

What are the Back ground processes in Oracle and what are they.

Answer :

This is one of the most frequently asked question.There are basically 9 Processes but in a general system we need to mention the first five background processes.They do the house keeping activities for the Oracle and are common in any system.
The various background processes in oracle are
a) Data Base Writer(DBWR) :: Data Base Writer Writes Modified blocks from Database buffer cache to Data Files.This is required since the data is not written whenever a transaction is committed.
b)LogWriter(LGWR) :: LogWriter writes the redo log entries to disk. Redo Log data is generated in redo log buffer of SGA. As transaction commits and log buffer fills, LGWR writes log entries into a online redo log file.
c) System Monitor(SMON) :: The System Monitor performs instance recovery at instance startup. This is useful for recovery from system failure
d)Process Monitor(PMON) :: The Process Monitor performs process recovery when user Process fails. Pmon Clears and Frees resources that process was using.
e) CheckPoint(CKPT) :: At Specified times, all modified database buffers in SGA are written to data files by DBWR at Checkpoints and Updating all data files and control files of database to indicate the most recent checkpoint
f)Archieves(ARCH) :: The Archiver copies online redo log files to archival storal when they are busy.
g) Recoveror(RECO) :: The Recoveror is used to resolve the distributed transaction in network
h) Dispatcher (Dnnn) :: The Dispatcher is useful in Multi Threaded Architecture
i) Lckn :: We can have upto 10 lock processes for inter instance locking in parallel sql.


Question 83 :

How many types of Sql Statements are there in Oracle

Answer :

There are basically 6 types of sql statments.They are
a) Data Definition Language(DDL) :: The DDL statements define and maintain objects and drop objects.
b) Data Manipulation Language(DML) :: The DML statements manipulate database data.
c) Transaction Control Statements :: Manage change by DML
d) Session Control :: Used to control the properties of current session enabling and disabling roles and changing .e.g. :: Alter Statements, Set Role
e) System Control Statements :: Change Properties of Oracle Instance .e.g.:: Alter System
f) Embedded Sql :: Incorporate DDL, DML and T.C.S in Programming Language.e.g:: Using the Sql Statements in languages such as 'C', Open, Fetch, execute and close


Question 84 :

What is a Transaction in Oracle

Answer :

A transaction is a Logical unit of work that compromises one or more SQL Statements executed by a single User. According to ANSI, a transaction begins with first executable statement and ends when it is explicitly committed or rolled back.
Key Words Used in Oracle
The Key words that are used in Oracle are ::
a) Committing :: A transaction is said to be committed when the transaction makes permanent changes resulting from the SQL statements.
b) Rollback :: A transaction that retracts any of the changes resulting from SQL statements in Transaction.
c) SavePoint :: For long transactions that contain many SQL statements, intermediate markers or savepoints are declared. Savepoints can be used to divide a transaction into smaller points.
d) Rolling Forward :: Process of applying redo log during recovery is called rolling forward.
e) Cursor :: A cursor is a handle ( name or a pointer) for the memory associated with a specific stamen. A cursor is basically an area allocated by Oracle for executing the Sql Statement. Oracle uses an implicit cursor statement for Single row query and Uses Explicit cursor for a multi row query.
f) System Global Area(SGA) :: The SGA is a shared memory region allocated by the Oracle that contains Data and control information for one Oracle Instance. It consists of Database Buffer Cache and Redo log Buffer.
g) Program Global Area (PGA) :: The PGA is a memory buffer that contains data and control information for server process.
g) Database Buffer Cache :: Database Buffer of SGA stores the most recently used blocks of database data. The set of database buffers in an instance is called Database Buffer Cache.
h) Redo log Buffer :: Redo log Buffer of SGA stores all the redo log entries.
i) Redo Log Files :: Redo log files are set of files that protect altered database data in memory that has not been written to Data Files. They are basically used for backup when a database crashes.
j) Process :: A Process is a 'thread of control' or mechanism in Operating System that executes series of steps.


Question 85 :

What are Procedure, functions and Packages ?

Answer :

Procedures and functions consist of set of PL/SQL statements that are grouped together as a unit to solve a specific problem or perform set of related tasks.
Procedures do not Return values while Functions return one One Value Packages :: Packages Provide a method of encapsulating and storing related procedures, functions, variables and other Package Contents


Question 86 :

What are Database Triggers and Stored Procedures

Answer :

Database Triggers :: Database Triggers are Procedures that are automatically executed as a result of insert in, update to, or delete from table.
Database triggers have the values old and new to denote the old value in the table before it is deleted and the new indicated the new value that will be used. DT are useful for implementing complex business rules which cannot be enforced using the integrity rules.We can have the trigger as Before trigger or After Trigger and at Statement or Row level. e.g:: operations insert,update ,delete 3 before ,after 3*2 A total of 6 combinatons
At statment level(once for the trigger) or row level( for every execution ) 6 * 2 A total of 12. Thus a total of 12 combinations are there and the restriction of usage of 12 triggers has been lifted from Oracle 7.3 Onwards.
Stored Procedures :: Stored Procedures are Procedures that are stored in Compiled form in the database.The advantage of using the stored procedures is that many users can use the same procedure in compiled and ready to use format.


Question 87 :

How many Integrity Rules are there and what are they

Answer :

There are Three Integrity Rules. They are as follows ::
a) Entity Integrity Rule :: The Entity Integrity Rule enforces that the Primary key cannot be Null
b) Foreign Key Integrity Rule :: The FKIR denotes that the relationship between the foreign key and the primary key has to be enforced.When there is data in Child Tables the Master tables cannot be deleted.
c) Business Integrity Rules :: The Third Intigrity rule is about the complex business processes which cannot be implemented by the above 2 rules.


Question 88 :

What are the Various Master and Detail Relation ships.

Answer :

The various Master and Detail Relationship are
a) NonIsolated :: The Master cannot be deleted when a child is exisiting
b) Isolated :: The Master can be deleted when the child is exisiting
c) Cascading :: The child gets deleted when the Master is deleted.


Question 89 :

What are the Various Block Coordination Properties

Answer :

The various Block Coordination Properties are
a) Immediate Default Setting. The Detail records are shown when the Master Record are shown.
b) Deffered with Auto Query Oracle Forms defer fetching the detail records until the operator navigates to the detail block.
c) Deffered with No Auto Query The operator must navigate to the detail block and explicitly execute a query


Question 90 :

What are the Different Optimization Techniques

Answer :

The Various Optimisation techniques are
a) Execute Plan :: we can see the plan of the query and change it accordingly based on the indexes
b) Optimizer_hint ::
set_item_property('DeptBlock',OPTIMIZER_HINT,'FIRST_ROWS');
Select /*+ First_Rows */ Deptno,Dname,Loc,Rowid from dept
where (Deptno > 25)
c) Optimize_Sql ::
By setting the Optimize_Sql = No, Oracle Forms assigns a single cursor for all SQL statements.This slow downs the processing because for evertime the SQL must be parsed whenver they are executed.
f45run module = my_firstform userid = scott/tiger optimize_sql = No
d) Optimize_Tp ::
By setting the Optimize_Tp= No, Oracle Forms assigns seperate cursor only for each query SELECT statement. All other SQL statements reuse the cursor.
f45run module = my_firstform userid = scott/tiger optimize_Tp = No


Question 91 :

How does one change an Oracle user's password?(for DBA)

Answer :

Issue the following SQL command:
ALTER USER IDENTIFIED BY ;
From Oracle8 you can just type "password" from SQL*Plus, or if you need to change another user's password, type "password user_name". Look at this example:
SQL> password
Changing password for SCOTT
Old password:
New password:
Retype new password:


Question 92 :

How does one create and drop database users?

Answer :

Look at these examples:
CREATE USER scott
IDENTIFIED BY tiger -- Assign password
DEFAULT TABLESACE tools -- Assign space for table and index segments
TEMPORARY TABLESPACE temp; -- Assign sort space
DROP USER scott CASCADE; -- Remove user
After creating a new user, assign the required privileges:
GRANT CONNECT, RESOURCE TO scott;
GRANT DBA TO scott; -- Make user a DB Administrator
Remember to give the user some space quota on its tablespaces:
ALTER USER scott QUOTA UNLIMITED ON tools;


Question 93 :

Who created all these users in my database?/ Can I drop this user? (for DBA)

Answer :

Oracle creates a number of default database users or schemas when a new database is created. Below are a few of them:
SYS/CHANGE_ON_INSTALL or INTERNAL
Oracle Data Dictionary/ Catalog
Created by: ?/rdbms/admin/sql.bsq and various cat*.sql scripts
Can password be changed: Yes (Do so right after the database was created)
Can user be dropped: NO
SYSTEM/MANAGER
The default DBA user name (please do not use SYS)
Created by: ?/rdbms/admin/sql.bsq
Can password be changed: Yes (Do so right after the database was created)
Can user be dropped: NO
OUTLN/OUTLN
Stored outlines for optimizer plan stability
Created by: ?/rdbms/admin/sql.bsq
Can password be changed: Yes (Do so right after the database was created)
Can user be dropped: NO
SCOTT/TIGER, ADAMS/WOOD, JONES/STEEL, CLARK/CLOTH and BLAKE/PAPER.
Training/ demonstration users containing the popular EMP and DEPT tables
Created by: ?/rdbms/admin/utlsampl.sql
Can password be changed: Yes
Can user be dropped: YES - Drop users cascade from all production environments
HR/HR (Human Resources), OE/OE (Order Entry), SH/SH (Sales History).
Training/ demonstration users containing the popular EMPLOYEES and DEPARTMENTS tables
Created by: ?/demo/schema/mksample.sql
Can password be changed: Yes
Can user be dropped: YES - Drop users cascade from all production environments
CTXSYS/CTXSYS
Oracle interMedia (ConText Cartridge) administrator user
Created by: ?/ctx/admin/dr0csys.sql
TRACESVR/TRACE
Oracle Trace server
Created by: ?/rdbms/admin/otrcsvr.sql
DBSNMP/DBSNMP
Oracle Intelligent agent
Created by: ?/rdbms/admin/catsnmp.sql, called from catalog.sql
Can password be changed: Yes - put the new password in snmp_rw.ora file
Can user be dropped: YES - Only if you do not use the Intelligent Agents
ORDPLUGINS/ORDPLUGINS
Object Relational Data (ORD) User used by Time Series, etc.
Created by: ?/ord/admin/ordinst.sql
ORDSYS/ORDSYS
Object Relational Data (ORD) User used by Time Series, etc
Created by: ?/ord/admin/ordinst.sql
DSSYS/DSSYS
Oracle Dynamic Services and Syndication Server
Created by: ?/ds/sql/dssys_init.sql
MDSYS/MDSYS
Oracle Spatial administrator user
Created by: ?/ord/admin/ordinst.sql
AURORA$ORB$UNAUTHENTICATED/INVALID
Used for users who do not authenticate in Aurora/ORB
Created by: ?/javavm/install/init_orb.sql called from ?/javavm/install/initjvm.sql
PERFSTAT/PERFSTAT
Oracle Statistics Package (STATSPACK) that supersedes UTLBSTAT/UTLESTAT
Created by: ?/rdbms/admin/statscre.sql
Remember to change the passwords for the SYS and SYSTEM users immediately after installation!
Except for the user SYS, there should be no problem altering these users to use a different default and temporary tablespace.


Question 94 :

How does one enforce strict password control? (for DBA)

Answer :

By default Oracle's security is not extremely good. For example, Oracle will allow users to choose single character passwords and passwords that match their names and userids. Also, passwords don't ever expire. This means that one can hack an account for years without ever locking the user.
From Oracle8 one can manage passwords through profiles. Some of the things that one can restrict:
. FAILED_LOGIN_ATTEMPTS - failed login attempts before the account is locked
. PASSWORD_LIFE_TIME - limits the number of days the same password can be used for authentication
. PASSWORD_REUSE_TIME - number of days before a password can be reused
. PASSWORD_REUSE_MAX - number of password changes required before the current password can be reused
. PASSWORD_LOCK_TIME - number of days an account will be locked after maximum failed login attempts
. PASSWORD_GRACE_TIME - number of days after the grace period begins during which a warning is issued and login is allowed
. PASSWORD_VERIFY_FUNCTION - password complexity verification script
Look at this simple example:
CREATE PROFILE my_profile LIMIT
PASSWORD_LIFE_TIME 30;
ALTER USER scott PROFILE my_profile;


Question 95 :

How does one switch to another user in Oracle? (for DBA)

Answer :

Users normally use the "connect" statement to connect from one database user to another. However, DBAs can switch from one user to another without a password. Of course it is not advisable to bridge Oracle's security, but look at this example: SQL> select password from dba_users where username='SCOTT';
PASSWORD
F894844C34402B67
SQL> alter user scott identified by lion;
User altered.

SQL> connect scott/lion
Connected.

REM Do whatever you like...
SQL> connect system/manager
Connected.

SQL> alter user scott identified by values 'F894844C34402B67';
User altered.
SQL> connect scott/tiger
Connected.
Note: Also see the su.sql script in the Useful Scripts and Sample Programs Page.


Question 96 :

What are snap shots and views

Answer :

Snapshots are mirror or replicas of tables. Views are built using the columns from one or more tables. The Single Table View can be updated but the view with multi table cannot be updated


Question 97 :

What are the OOPS concepts in Oracle.

Answer :

Oracle does implement the OOPS concepts. The best example is the Property Classes. We can categorize the properties by setting the visual attributes and then attach the property classes for the objects. OOPS supports the concepts of objects and classes and we can consider the property classes as classes and the items as objects


Question 98 :

What is the difference between candidate key, unique key and primary key

Answer :

Candidate keys are the columns in the table that could be the primary keys and the primary key is the key that has been selected to identify the rows. Unique key is also useful for identifying the distinct rows in the table.)


Question 99 :

What is concurrency

Answer :

Concurrency is allowing simultaneous access of same data by different users. Locks useful for accesing the database are
a) Exclusive
The exclusive lock is useful for locking the row when an insert,update or delete is being done.This lock should not be applied when we do only select from the row.
b) Share lock
We can do the table as Share_Lock as many share_locks can be put on the same resource.


Question 100 :

Previleges and Grants

Answer :

Previleges are the right to execute a particulare type of SQL statements. e.g :: Right to Connect, Right to create, Right to resource Grants are given to the objects so that the object might be accessed accordingly.The grant has to be given by the owner of the object