Tuesday, February 16, 2016

Oracle FAQs

1.     WHAT IS DATA OR INFORMATION?
Ans: The Matter that we feed into the Computer is called Data or Information.

2.     WHAT IS DATABASE?
Ans: The Collection of Interrelated Data is called Data Base.

3.     WHAT IS A DATABASE MANAGEMENT SYSTEM (DBMS) PACKAGE?
Ans: The Collection of Interrelated Data and some Programs to access
the Data is Called Data Base Management System (DBMS).

4.     WHEN CAN WE SAY A DBMS PACKAGE AS RDBMS?
Ans: For a system to Qualify as RELATIONAL DATABASE MANAGEMENT system,
it must use its RELATIONAL facilities to MANAGE the DATABASE.

5.     WHAT IS ORDBMS?
Ans: Object (oriented) Relational Data Base Management System is one
that can store data, the relationship of the data, and the behavior of the data
(i.e., the way it interacts with other data).

6.     NAME SOME CODD'S RULES.
Ans: Dr. E.F. Codd presented 12 rules that a database must obey if it
is to be considered truly relational. Out those,  some are as follows
a)     The rules stem from a single rule- the ‘zero rule’: For a system to Qualify as RELATIONAL DATABASE MANAGEMENT system, it must use its RELATIONAL facilities
to MANAGE the DATABASE.
b)     Information Rule: Tabular Representation of Information.
c)     Guaranteed Access Rule: Uniqueness of tuples for guaranteed accessibility.
d)     Missing Information Rule: Systematic representation of missing information as NULL   Values.
e)     Comprehensive Data Sub-Language Rule: QL to support Data definition,
View definition, Data manipulation, Integrity, Authorization and Security.

7.     WHAT ARE HIERARCHICAL, NETWORK, AND RELATIONAL DATABASE MODELS?
Ans: a) Hierarchical Model: The Hierarchical Model was introduced in
the Information Management System (IMS) developed by IBM in 1968. In this data is organized as a tree structure. Each tree is made of nodes and branches.
The nodes of the tree represent the record types and it is a collection
of data attributes entity at that point. The topmost node in the structure is called the root. Nodes succeeding lower levels are called children.

b) Network Model: The Network Model, also called as the CODSYL database
structure, is an improvement over the Hierarchical mode, in this model concept of parent and child is expanded to have multiple parent-child relationships, i.e. any child can be subordinate to many different parents (or nodes). Data is represented by
collection of records, and relationships among data are represented by
links. A link is an association between precisely two records. Many-to-many relationships can exists between the parent and child.

c) Relational Model: The Relational Database Model eliminates the need
for explicit parent-child relationships. In RDBMS, data is organized in two-dimensional tables consisting of relational, i.e. no pointers are maintained between tables.

8.     WHAT IS DATA MODELING?
Ans: Data Modeling describes relationship between the data objects. The  relationships between the collections of data in a system may be graphically represented using data modeling.

9.     DEFINE ENTITY, ATTRIBUTE AND RELATIONSHIP.
Ans: Entity: An Entity is a thing, which can be easily identified. An entity is any object, place, person, concept or activity about which an enterprise records data.
Attribute: An attribute is the property of a given entity.
Relationship: Relationship is an association among entities.

10.   WHAT IS ER-MODELING?
Ans: The E-R modeling technique is the Top Down Approach. Entity
relationship is technique for analysis and logical modeling of a system’s data requirements. It is the most widely used and has gained acceptance as the ideal database design. It uses three basic units: entities, their attributes and the relationship that exists between
 the entities. It uses a graphical notation for representing these.

11.   WHAT IS NORMALIZATION?
Ans: Normalization is a step-by-step decomposition of complex records
into simple records.

12.   WHAT ARE VARIOUS NORMAL FORMS OF DATA?
Ans: The First Normal Form 1NF,
The Second Normal Form     2NF,
The Third Normal Form        3NF,
The Boyce and Codd Normal Form      BC NF.

13.   WHAT IS DENORMALIZATION?
Ans: The intentional introduction of redundancy to a table to improve
performance is called DENORMALIZATION.

14.   WHAT ARE 1-TIER, 2-TIER, 3-TIER OR N-TIER DATABASE ARCHITECTURES?
Ans: 1-Tier Database Architecture is based on single system, which acts
as both server and client.
2-Tier Architecture is based on one server and client.
3-Tier Architecture is based on one server and client out that on client act as a remote system.
N-Tier Architecture is based on N no. Of servers and N no. Of clients.

15.   WHAT ARE A TABLE, COLUMN, AND RECORD?
Ans: Table:  A Table is a database object that holds your data. It is made up of many columns. Each of these columns has a data type associated with it.
Column: A column, referred to as an attribute, is similar to a field in the file system.
Record: A row, usually referred to as tuple, is similar to record in the file system.

16.   WHAT IS DIFFERENCE BETWEEN A PROCEDURAL LANGUAGE AND A NON-PROCEDURAL LANGUAGE?
Ans:
Procedural Language    NON-Procedural Language
A program in this implements a step-by-step algorithm to solve the problem. It contains what to do but not how to do .

17.WHAT TYPE OF LANGUAGE  "SQL" IS?
Ans: SQL is a Non-procedural, 4th generation Language,/ which concerts what to do rather than how to do any process.

18.   CLASSIFICATION OF SQL COMMANDS?
Ans:
DDL (Data Definition Language) DQL [Data Querying Lnaguage ]
DML (Data Manipulating Language)  DCL (Data Control Language)    
TCL(Data Transaction Language)
Create  Alter Drop Truncate Rename, Select , Insert  Update Delete Merge , Grant Revoke , Rollback Commit savepoint

19.   WHAT IS DIFFERENCE BETWEEN DDL AND DML COMMANDS?
Ans: For DDL commands autocommit is ON implicitly whereas For DML commands autocommit is to be turned ON explicitly.

20.   WHAT IS DIFFERENCE BETWEEN A TRANSACTION AND A QUERY?
Ans: A Transaction is unit of some commands where as Query is a single line request for the information from the  database.

21.   WHAT IS DIFFERENCE BETWEEN TRUNCATE AND DELETE COMMANDS?
Ans: Truncate Command will delete all the records where as Delete
Command will delete specified or all the records depending only on the condition given.

22.   WHAT IS DIFFERENCE BETWEEN UPDATE AND ALTER COMMANDS?
Ans: Alter command is used to modify the database objects where as the
Update command is used to modify the values of a data base objects.

23.   WHAT ARE COMMANDS OF DCL CATEGORY?
Ans: Grant and Revoke are the two commands belong to the DCL Category.

24.   WHICH IS AN EFFICIENT COMMAND - TRUNCATE OR DELETE? WHY?
Ans: Delete is the efficient command because using this command we can delete only those records that are not really required.

25.   WHAT ARE RULES FOR NAMING A TABLE OR COLUMN?
Ans: 1) Names must be from 1 to 30 bytes long.
2) Names cannot contain quotation marks.
3) Names are not case sensitive.
4) A name must begin with an alphabetic character from your database character set and the characters $ and #.
 But these characters are discouraged.
5) A name cannot be ORACLE reserved word.
6) A name must be unique across its namespace. Objects in the name space must have different names.
7) A name can be enclosed in double quotes.

26.   HOW MANY COLUMNS CAN A TABLE HAVE?
Ans: A Table can have 1000 columns.

27.   WHAT ARE DIFFERENT DATATYPES SUPPORTED BY SQL?
Ans: Char (size), Nchar (size), Varchar2 (size), Nvarchar2 (size) data types for character values,
Number (precision, scale), Number, Number (n), Float, Float (binary precision) data types for numerical values, Date data type for date values,
Long, Raw (size), Long Raw, Clob, Blob, Nclob, Bfile for large objects.

28.   WHAT IS DIFFERENCE BETWEEN LONG AND LOB DATATYPES?
Ans:
LOB LONG
1) The maximum size is 4GB.
2) LOBs (except NCLOB) can be attributes of an object type.
3) LOBs support random access to data.
4) Multiple LOB columns per table or LOB attributes in an object type.   
1) The maximum size is 2GB. 
2) LONGs cannot.   
3) LONGs support only sequential access.
4) Only one LONG column was allowed in a table

29.   WHAT IS DIFFERENCE BETWEEN CHAR AND VARCHAR2 DATATYPES?
Ans: Varchar2 is similar to Char but can store variable no. Of characters and while querying the table varchar2  trims the extra spaces from the column and fetches the rows that exactly match the criteria.

30.  HOW MUCH MEMORY IS ALLOCATED FOR DATE DATATYPE? WHAT IS DEFAULT  DATE  FORMAT IN ORACLE?
Ans: For Date data type oracle allocates 7 bytes Memory.
  Default Date Format is: DD-MON-YY.

31.   WHAT IS RANGE FOR EACH DATATYPE OF SQL?
Ans:
Datatype Range
Char   Varchar2  Number    Float     LONG, RAW, LONGRAW  Large Objects
(LOB’s) 2000 bytes  4000 bytes 
Precision 1 to 38 Scale -84 to 127  Precision 38 decimals Or 122 binary
precision   2 GB  4GB

32.   HOW TO RENAME A COLUMN?
Ans: We can’t rename a Column of a table directly. So we follow the following steps.
To Rename a Column:
a)     Alter the table specifying new column name to be given and data type.
b)     Then copy the values in the column to be renamed into new column.
c)     drop the old column.

33.   HOW TO DECREASE SIZE OR CHANGE DATATYPE OF A COLUMN?
Ans: To Decrease the size of a Data type of a column
i.      Truncate the table first.
ii.     Alter the table column whose size is to be decreased using the same name and data type but new size.

34.   WHAT IS A CONSTRAINT? WHAT ARE ITS VARIOUS LEVELS?
Ans: Constraint: Constraints are representators of the column to
enforce data entity and consistency.There r two levels 1)Column-level constraints 2)Table-level constraints.

35.   LIST OUT ALL THE CONSTRAINTS SUPPORTED BY SQL.
Ans: Not Null, Unique, Check, Primary Key and Foreign Key or Referential Integrity.

36.   WHAT IS DIFFERENCE BETWEEN UNIQUE+NOT NULL AND PRIMARY KEY?
Ans: Unique and Not Null is a combination of two Constraints that can be present any number of times in a table and can’t be a referential key to any column of an another table where as Primary Key is single Constraint that can be only once for table and can be a referential key to a column of another table becoming a referential integrity.

37.   WHAT IS A COMPOSITE PRIMARY KEY?
Ans: A Primary key created on combination of columns is called Composite Primary Key.

38.   WHAT IS A CANDIDATE COLUMN? HOW MANY CANDIDATE COLUMNS CAN BE
POSSIBLE PER COMPOSITE PRIMARY KEY?
Ans: It is a part of composite primary key.  Maximum 32 candidate key can be there in composite primary key.

39.   HOW TO DEFINE A NULL VALUE?
Ans: A NULL value is something which is unavailable, it is neither zero nor a space and any mathematical calculation with NULL is always NULL.

40. WHAT IS NULL?  A CONSTRAINT OR DEFAULT VALUE?
Ans: It is a default value.

41. WHAT IS DEFAULT VALUE FOR EVERY COLUMN OF A TABLE?
Ans: NULL.

42. WHAT IS CREATED IMPLICITLY FOR EVERY UNIQUE AND PRIMARY KEY  COLUMNS?
Ans: Index.

43. WHAT ARE LIMITATIONS OF CHECK CONSTRAINT?
Ans: In this we can't specify Pseudo Columns like sysdate etc.

44. WHAT IS DIFFERENCE BETWEEN REFERENCES AND FOREIGN KEY CONSTRAINT?
Ans: References is used as column level key word where as foreign key
is used as table level constraint.

45. WHAT IS "ON DELETE CASCADE"?
Ans: when this key word is included in the definition of a child table
then whenever the records from the parent table is deleted automatically the respective values in the child table will be deleted.

46. WHAT IS PARENT-CHILD OR MASTER-DETAIL RELATIONSHIP?
Ans: A table which references a column of another table(using References)is called  as a child table(detail table) and a table  which is being referred  is called Parent (Master) Table .

47. HOW TO DROP A PARENT TABLE WHEN IT’S CHILD TABLE EXISTS?
Ans: Using "on delete cascade".

48. IS ORACLE CASE SENSITIVE?
Ans: NO

49. HOW ORACLE IDENTIFIES EACH RECORD OF TABLE UNIQUELY?
Ans: By Creating indexes and reference IDs.

50. WHAT IS A PSEUDO-COLUMN? NAME SOME PSEUDO-COLUMNS OF ORACLE?
Ans: Columns that are not created explicitly by the user and can be
used explicitly in queries  are called Pseudo-Columns.
Ex:currval,nextval,sysdate,new,old,sqlcode,sqlerrm,rownum,rowid,level

51. WHAT FOR "ORDER BY" CLAUSE FOR A QUERY?
Ans: To arrange the query result in a specified
Order (ascending,descending) by default it takes ascending order.

52. WHAT IS "GROUP BY" QUERIES?
Ans: To group the query results based on condition.

53. NAME SOME AGGREGATE FUNCTIONS OF SQL?
Ans: AVG, MAX, SUM, MIN,COUNT.

54. WHAT IS DIFFERENCE BETWEEN COUNT (), COUNT (*) FUNCTIONS?
Ans: Count () will count the specified column whereas count (*) will
count total no. of rows in a table.

55. WHAT FOR ROLLUP AND CUBE OPERATORS ARE?
Ans: To get subtotals and grand total of values of a column.

56. WHAT IS A SUB-QUERY?
Ans: A query within a query  is called a sub query where the result of
inner query will be used by the  outer query.



57. WHAT ARE SQL OPERATORS?
Ans: Value (), Ref () is SQL operator. ( Used with Objects )

 58. EXPLAIN "ANY","SOME","ALL","EXISTS" OPERATORS?
  Ans: Any: The Any (or it’s synonym SOME) operator computes the lowest
value from the set and compares a value to each returned by a sub query.

All: ALL compares a value to every value returned by SQL.
Exists: This operator produces a BOOLWAN results. If a sub query
produces any result then it evaluates it to TRUE else it evaluates it to FALSE.

59. WHAT IS A CORRELATED SUB QUERY, HOW IT IS DIFFERENT FROM A NORMAL
SUB QUERY?
Ans: A correlated subquery is a nested subquery, which is executed once
for each ‘Candidate row’ by the main query, which on execution uses a value from a column in the outer query. In normal sub query the result of inner query is dynamically substituted in the condition of the outer query where as in a correlated subquery, the column
value used in inner query refers to the column value present in the
outer query forming a correlated subquery.

 60. WHAT IS A JOIN - TYPES OF JOINS?
Ans: A join is used to combine two or more tables logically to get
query results.

    There are four types of Joins namely
     EQUI Join
     NON-EQUI Join
     SELF Join
     OUTER Join.

  61. WHAT ARE MINIMUM REQUIREMENTS FOR AN EQUI-JOIN?
Ans: There shold be atleast one common column between the joining tables.

  62. WHAT IS DIFFERENCE BETWEEN LEFT, RIGHT OUTER JOIN?
Ans:If there r any values in one table that do not have corresponding values in the other,in an equi join that row will not be selected.Such rows can be forcefully selected by using outer join symbol(+) on either of the sides(left or right)  based on the requirement. 

  63. WHAT IS DIFFERENCE BETWEEN EQUI AND SELF JOINS?
Ans: SELF JOIN is made within the table whereas
     EQUI JOIN is made between  different tables having common column.

  64. WHAT ARE "SET" OPERATORS?
Ans: UNION ALL,UNION, INTERSECT ,MINUS are SET OPERATORS.

  65. WHAT IS DIFFERENCE BETWEEN "UNION" AND "UNION ALL"
OPERATORS?
Ans: UNION will return the values distinctly whereas UNION ALL will
return even duplicate values.

  66. NAME SOME NUMBER, CHARACTER, DATE, CONVERSION, OTHER
FUNCTIONS.
Ans: Number Functions:
                Round (m, [n]),  Trunc (m, [n]),  Power (m, n),  Sqrt(n),
                Abs (m), Ceil (m),  Floor (m), Mod (m, n) ,sign(n)                                 

      Character Functions:
                Chr (x), Concat (string1, string2), Lower (string)
                      Upper (string), Substr (string, from_str, to_str), ASCII (string)
                      Length (string), Initcap (string). 

  Date Functions:
                 Sysdate, Months between (d1, d2), To_char (d, format)
                 Last day (d), Next_day (d, day).add_months(d,n), Extract
      Conversion Functions:     To_char,  To_date, To_number

  67. WHAT IS DIFFERENCE BETWEEN MAX () AND GREATEST () FUNCTIONS?
Ans: MAX is an aggregate function which takes only one column name of a table as parameter whereas Greatest is a general function which can take any number of values and column names from dual and table respectively.

  68. WHAT FOR NVL () FUNCTION IS?
Ans: NVL Function helps in substituting a value in place of a NULL.

  69. WHAT FOR DECODE () FUNCTION IS?
Ans: It is substitutes value basis and it actually does an
'if-then-else' test.

  70. WHAT IS DIFFERENCE BETWEEN TRANSLATE () AND REPLACE () FUNCTIONS?
Ans: Translate()   is a superset of functionality provided by Replace().

  71. WHAT IS DIFFERENCE BETWEEN SUBSTR () AND INSTR () FUNCTIONS?
Ans: Substr() will return the specified part of a string whereas
  
  Instr() return the position of the specified part of the string.

  72. WHAT IS A JULIAN DAY NUMBER?
Ans: It will return count of the no. Of days between January 1, 4712 BC
and the given date.

  73. HOW TO DISPLAY TIME FROM A DATE DATA?
Ans: By using time format as 'hh [hh24]: mi: ss' in to_char() function.

  74. HOW TO INSERT DATE AND TIME INTO A DATE COLUMN?
Ans: By using format 'dd-mon-yy hh [hh24]: mi: ss' in to_date() function.

  75. WHAT IS DIFFERENCE BETWEEN TO_DATE () AND TO_CHAR () CONVERSION
FUNCTIONS?
Ans: To_date converts character date to date format whereas
     To_char function converts date or numerical values to characters.

  76. WHAT IS A VIEW? HOW IT IS DIFFERENT FROM A TABLE?
Ans: View is database object, which exists logically but contains no
physical data and manipulates the base table.
View is saved as a select statement in the database and contains no
physical data whereas Table exists physically.

  77. WHAT IS DIFFERENCE BETWEEN SIMPLE AND COMPLEX VIEWS?
Ans: Simple views can be modified whereas Complex views (created based
on more than one table) cannot be modified.

  78. WHAT IS AN INLINE VIEW?
Ans: Inline view is basically a subquery with an alias that u can use
like a view inside a SQL statement. It is not a schema object like SQL-object.

  79. HOW TO UPDATE A COMPLEX VIEW?
Ans: Using  'INSTEAD OF' TRIGGERS Complex views can be Updated.

  80. WHAT FOR "WITH CHECK OPTION" FOR A VIEW?
Ans: "WITH CHECK OPTION" clause specifies that inserts and updates r performed through the view r not allowed to create rows  which the view cannot select and therefore allows integrity constraints and data validation checks to be enforced on data being inserted or updated.

81. WHAT IS AN INDEX? ADVANTAGE OF AN INDEX
Ans: An Index is a database object used n Oracle to provide quick
access to rows in a table. An Index increases the performance of the database.

  82. WHAT IS A SEQUENCE? PSEUDO-COLUMNS ASSOCIATED WITH SEQUENCE?
Ans: Sequence is a Database Object used to generate unique integers  to use as primary keys. Nextval, Currval are the Pseudo Columns associated with the sequence.

**83. WHAT IS A CLUSTER? WHEN TO USE A CLUSTER? HOW TO DROP A CLUSTER
WHEN CLUSTERED TABLE EXISTS?
Ans: Cluster and Indexes are transparent to the user. Clustering is a
method of storing tables that are intimately related and are often joined together into the same area on the disk.
When cluster table exists then to drop cluster we have to drop the table first then only cluster is to be dropped.

  84. WHAT IS A SNAPSHOT OR MATERIALIZED VIEW?
Ans: Materialized views can be used to replicate data. Earlier the data
was replicated through CREATE SNAPSHOT command. Now CREATE MATERIALIZED VIEW can be used as synonym for CREATE SNAPSHOT. Query performance is improved using the materialized view as these views pre calculate expensive joins and aggregate operations on the table.

85. WHAT IS A SYNONYM?
Ans:  A Synonym is a database object that allows you to create alternate names for Oracle tables and views. It is an alias for a table, view, snapshot, sequence, procedure, function or
package.

  86. WHAT IS DIFFERENCE BETWEEN PRIVATE AND PUBLIC SYNONYM?
Ans: Only the user or table owner can reference Private synonym whereas
any user can reference the Public synonym.

  87. WHAT IS DIFFERENCE BETWEEN "SQL" AND "SQL*PLUS" COMMANDS?
Ans:  SQL commands are stored in the buffer whereas SQL*PLUS are not.

**88. NAME SOME SQL*PLUS COMMANDS?
Ans:        DESC [CRIBE], START, GET, SAVE, / are SQL*PLUS COMMANDS.

  89. WHAT ARE "SQL*PLUS REPORTING" COMMANDS?
Ans: SPOOL file-name, SPOOL OFF, TTITLE, BTITLE, BREAK ON, COMPUTE <any
aggregate function> OF <column name> [break] ON <column name> etc are SQL*PLUS REPORTING COMMANDS.

  90. WHAT ARE SYSTEM AND OBJECT PRIVILEGES?
Ans: Connect and Resource etc are System Privileges.
Create <object>, Select, Insert, Alter etc are Object Privileges.
       
  91. WHAT FOR DCL COMMANDS ARE?
Ans: Commit, Rollback are DCL commands.

  92. WHAT FOR GRANT COMMAND WITH "WITH GRANT OPTION"?
Ans: “With Grant Option” with Grant Command gives privileges to the
user to grant privileges to other user(s)
among the privileges he/she has.

  93. HOW TO CHANGE PASSWORD OF A USER?
Ans: Using Password command or
Using ALTER USER <user name> IDENTIFIED BY <new password> COMAND.

94. WHAT IS A SCHEMA AND SCHEMA OBJECTS?
Ans: A schema is a collection of logical structures of data, or schema


objects. A schema is owned by the database user and has the same name as that of user. Each user owns a single schema. Schema objects include following
type of objects Clusters, Database Links, Functions, Indexes, Packages,
Procedures, Sequences, Synonyms, Tables, Database Triggers, Views.

  **95. HOW TO STARTUP AND SHUTDOWN ORACLE DATABASE?
Ans: Startup and Shutdown Oracle database can be done by only the
administator. Startup is done by using STARTUP command and Shutdown is done by SHUTDOWN command

  96. WHAT IS A SESSION?
Ans: The period between Login and Logoff on schema.

  97. WHAT IS A CLIENT PROCESS? WHAT IS A SERVER PROCESS?
Ans: ref: 172 Q & A.

  98. HOW TO MAKE EVERY DML OPERATION AS AUTO COMMIT?
Ans: By using SET AUTOCOMMIT ON command.

  99. HOW TO DISPLAY DATA PAGE WISE IN SQL?
Ans: By using SET PAUSE ON command.

100. HOW TO CHANGE LINE SIZE, PAGE SIZE AND SQL PROMPT?
Ans: By using SET LINESIZE <value>, SET PAGESIZE <value>,
     SET SQLPROMPT <new prompt>.

101. HOW PL/SQL IS DIFFERENT FROM SQL?
Ans: SQL is non-procedural language whereas PL/SQL is procedural
language that includes features and design of programming language.

102. WHAT IS ARCHITECTURE OF PL/SQL?
Ans:   Give picture & Explain

103. WHAT IS A PL/SQL BLOCK?
Ans:        DECLARE
           <declarations>
        BEGIN
           <Exececutable Statements>
        EXCEPTION
           <Exception Handler(s)>
        END;

104. WHAT ARE DIFFERENT TYPES OF PL/SQL BLOCKS?
Ans: DECLARE BLOCK: In this block all the declarations of the variable
used in the program is made. If no variables are used this block will become optional.
          BEGIN BLOCK: In this block all the executable statements are
          placed. This block is Mandatory.
          EXCEPTION BLOCK: In this block all the exceptions are handled.
                     This block is also very optional.
          END: Every begin must be ended with this END; statement.

  Anonymous & Named Blocks


105. WHAT ARE COMPOSITE DATA TYPES?
Ans: Records, Tables are two Composite data types.

106. WHAT IS SCOPE OF A VARIABLE IN PL/SQL BLOCK?
Ans: The visuability and accessibility of a variable within the
block(s) is called scope of a variable.

107. WHAT IS A NESTED BLOCK?
Ans: A block within a block is called Nested Block.


108. WHAT IS A PL/SQL ENGINE?
Ans:  The PL/SQL engine accepts any valid PL/SQL block as input, executes the procedural part of the statements and sends the SQL statements to the SQL statement executor in the Oracle server.

109. WHAT IS DEFAULT VALUE FOR A NUMERIC PL/SQL VARIABLE?
Ans: NULL

110. WHAT IS DIFFERENCE BETWEEN SIMPLE LOOP AND A FOR LOOP?
Ans: Simple requires declaration of variables used in it and exit
condition but For Loop doesn’t require this.

111. WHAT IS A CURSOR? STEPS TO USE A CURSOR?
Ans: Cursor is Private SQL area in PL/SQL.
     Declare the Cursor,
     Open the Cursor,
     Fetch values from SQL into the local Variables,
     Close the Cursor.

112. HOW MANY TYPES OF CURSORS ARE SUPPORTED BY ORACLE?
Ans:  There are two types of cursors namely Implicit Cursor, Explicit Cursor.

113. WHAT IS A CURSOR FOR LOOP?
Ans: Cursor For Loop is shortcut process for Explicit Cursors because
the Cursor is Open, Rows are fetched once for each iteration and the cursor is closed automatically when all the rows have been processed.

114. WHAT ARE CURSOR ATTRIBUTES?
Ans: %Found
     %NotFound
     %IsOpen
     %RowCount are the cursor attributes.

115. WHAT IS USE OF CURSOR WITH "FOR UPDATE OF" CLAUSE?
Ans: This Clause stop accessing of other users on the particular
columns used by the cursor until the COMMIT is issued.

116. WHAT IS AN EXCEPTION? HOW IT IS DIFFERENT FROM ERROR?
Ans: Whenever an error occurs Exception raises. Error is a bug whereas the Exception is a warning or error condition.

117. NAME SOME BUILT-IN EXCEPTIONS.
Ans: Too_Many_Rows,  No_Data_Found,   Zero_Divide,    Not_Logged_On
     Storage_Error,    Value_Error etc.

118. HOW TO CREATE A USER-DEFINED EXCEPTION?
Ans: User-Defined Exception is created as follows:
      DECLARE
        <exception name> EXCEPTION;
        - - - - - - - - - ;
        - - - - - - - - -;
        BEGIN
        - - - - - - - - -;
        - - - - - - - - -;
        RAISE <exception name>;
        EXCEPTION
        WHEN <exception name> THEN
        - - - - - - - - -;
        - - - - - - - - -;
        END;



119. WHAT IS "OTHERS" EXCEPTION?
Ans: It is used to along with one or more exception handlers.
     This will handle all the errors not already handled in the block.

120. WHAT IS SCOPE OF EXCEPTION HANDLING IN NESTED BLOCKS?
Ans: Exception scope will be with in that block in which exception
handler is written.

121. WHAT IS A SUB-PROGRAM?
Ans: A SUBPROGRAM IS A PL/SQL BLOCK, WHICH WILL BE INVOKED BY TAKING
PARAMATERS.

122. WHAT ARE DIFFERENT TYPES OF SUB-PROGRAMS?
Ans: THEY R TWO TYPES: 1) PROCEDURE 2) FUNCION.

123. HOW A PROCEDURE IS DIFFERENT FROM A FUNCTION?
Ans: Function has return key word and returns a value whereas a
Procedure doesn’t return any value.

124. WHAT ARE TYPES OF PARAMETERS THAT CAN BE PASSED TO FUNCTION OR
PROCEDURE?
Ans: IN, IN OUT, OUT.

125. WHAT IS "IN OUT" PARAMETER?
Ans: A parameter, which gets value into the Procedure or Function and
takes the value out of the Procedure or
Function area, is called IN OUT parameter.

126. DOES ORACLE SUPPORTS PROCEDURE OVERLOADING?
Ans:  NO.

127. WHAT IS A PACKAGE AND PACKAGE BODY?
Ans: Package is declarative part of the functions and procedures stored
in that package and package body is
the definition part of the functions and procedures of that package.

128. WHAT IS ADVANTAGE OF PACKAGE OVER PROCEDURE OR FUNCTION?
Ans: Packages provides Functions or Procedures Overloading facility and
security to those Functions or
Procedures.

129. IS IT POSSIBLE TO HAVE A PROCEDURE AND A FUNCTION WITH THE SAME
NAME?
Ans: NO if it is out side a Package, YES if it is within a Package.

130. DOES ORACLE SUPPORTS RECURSIVE FUNCTION CALLS?
Ans: YES.

131. WHAT IS A TRIGGER? HOW IT IS DIFFERENT FROM A PROCEDURE?
Ans: Trigger:  A Trigger is a stored PL/SQL program unit associated
with a specific database table.
     Procedure: A Procedure is to be explicitly called by the user
whereas Triggers are automatically called implicitly
    by Oracle itself whenever event Occurs.

132. WHAT IS DIFFERENCE BETWEEN A TRIGGER AND A CONSTRAINT?
Ans: Constraints are always TRUE whereas Triggers are NOT always TRUE
and Constraints has some limitations whereas Trigger has no limitations.

133. WHAT ARE DIFFERENT EVENTS FOR A TRIGGER AND THEIR SCOPES?
Ans: Insert, Update or Delete.




134. WHAT IS DIFFERENCE BETWEEN TABLE LEVEL AND ROW LEVEL TRIGGERS?
Ans: Table level Triggers execute once for each table based transaction
whereas Row level Triggers will execute once FOR EACH ROW.

** 135. WHAT ARE AUTONOMOUS TRIGGERS?
Ans: Supports to provide Commit statement in Triggers. Triggers a declared as independent
         Transactions.

136. WHAT IS AN "INSTEAD OF" TRIGGER?
Ans: These Triggers are used with the Complex Views only to make
possible of Insert, Update and Delete on those Views.

** 137. HOW MANY TRIGGERS CAN BE CONFIGURED ON A TABLE AND VIEW?
Ans: 18 Triggers

138. WHAT IS "TABLE MUTATING" ERROR? HOW TO SOLVE IT?
Ans: ORA-04091:   Table name is mutating, trigger/function may not see it
Cause : A trigger or a user-defined PL/SQL function that is referenced
in the statement attempted to query or modify a table that was in the middle of being modified by the statement that fired the trigger.
Action : Rewrite the trigger or function so it does not read the table.

139. WHEN TO USE ":NEW" AND ":OLD" SPECIFIERS?
Ans:  The prefix :old is used to refer to values already present in the
table. The prefix :new is a correlation name that refers to the new value that  is inserted / updated.

** 141. HOW TO CREATE A USER-DEFINED VARIABLE IN PL/SQL?
Ans:  Define variable in declaration section

142. HOW TO CREATE AN ARRAY VARIABLE IN PL/SQL?
Ans: Using CREATE [OR REPLACE] TYPE <type name>
AS VARRAY (size) OF ELEMENT_TYPE (NOT NULL) Command; 

**143. HOW TO MAKE A USER-DEFINED DATA TYPE GLOBAL IN PL/SQL?
Ans: Declare the variable in a Package

144. HOW TO CREATE AN OBJECT IN ORACLE?
Ans: Using CREATE [OR REPLACE] TYPE <type name> AS OBJECT (ATTRIBUTE
NAME DATA TYPE,..) Command  

145. WHAT IS A TRANSIENT AND PERSISTENT OBJECT?
Ans: The Object created in a table is called Persistent Object.
     Object created on execution of PL/SQL block is called Transient Object.

**146. WHAT IS A COLUMN OBJECT AND TABLE OBJECT?
Ans: A Column Object is only a Column of a table.
  
147. HOW TO GRANT PERMISSION ON AN OBJECT TO OTHER USER?
Ans: GRANT <permission> ON <object name> TO <user name>.

148. WHAT IS A COLLECTION OF ORACLE?
Ans: Varray, Nested Table is a collection of Oracle.

149. WHAT IS DIFFERENCE BETWEEN VARRAY AND NESTED TABLE?
Ans: Varray has a fixed size.
     Nested tables can carry any number of values.




150. HOW TO MODIFY CONTENTS OF A VARRAY IN ORACLE?
Ans: To modify a stored VARRAY it has to selected into a
     PL/SQL variable and then inserted back into the table.

151. WHAT IS USE OF "THE" OPERATOR FOR NESTED TABLE?
Ans: THE operator allows nested tables to be manipulated using DML when
it is stored in a Table.

152. WHICH PACKAGE IS USED FOR FILE INPUT/OUTPUT IN ORACLE?
Ans: UTL_FILE Package is used for File input/output in Oracle.

153. NAME SOME METHODS AND PROCEDURES OF FILE I/O PACKAGE?
Ans: FOPEN, FCLOSE,  FFLUSH, IS_OPEN, GET_LINE, PUT_LINE, PUTF, NEW_LINE

**154. WHAT IS SQLJ? HOW IT IS DIFFERENT FROM JDBC CONNECTIVITY?
Ans: SQLJ is basically a Java program containing embedded static SQL
statements that are compatible with Java design philosophy.

155. WHAT IS AN ITERATOR? Name some TYPES OF ITERATORS?
Ans: SQLJ Iterators are basically record groups generated during
transaction, which requires manipulation of more than one records from one or more tables. There are two types Iterators namely Named Iterator and Positional Iterator.

** 156. WHAT ARE DIFFERENT STEPS TO WRITE A DYNAMIC SQL PROGRAM?
Ans:  Eg: char c_sqlstring[]={“DELETE FROM sailors WHERE rating>5”};
EXEC SQL PREPARE readytogo FROM :c_sqlstring;
EXEC SQL EXECUTE readytogo;

157. WHAT IS TABLE PARTITIONING AND INDEX PARTITIONING?
Ans: Oracle8 allows tables and Indexes to be partitioned or broken up into smaller parts based on range of key values. Partitioning is a “divide and conquer” strategy that improves administration and performance in data warehouse and OLTP systems.

159. WHAT IS PHYSICAL MEMORY STRUCTURE OF ORACLE?
Ans: The basic oracle memory structure associated with Oracle includes:
Software Code Areas The System Global Area (SGA) ,The Database Buffer Cache
The shared Pool, The Program Global Areas (PGA), Stack Areas ,Data Areas, Sort Areas

160. WHAT IS LOGICAL MEMORY STRUCTURE OF ORACLE?
Ans: Database, Tablespace , DB Object, Segment, Extents

161. WHAT IS SGA?
Ans: A System Global Area is a group of shared memory allocated by
Oracle that contains data and control information for one Oracle database instance. IF the multiple users are concurrently connected to the same instance, the data in the instance’s SGA is “shared” among the users.
Consequently, the SGA is often referred to as either the “system Global Area” or the “Shared
Global Area”.

162. WHAT IS PGA?
Ans: The Program Global Area is a memory buffer that contains data and
control information for a server process. A PGA is created by Oracle when a server process is started. The information in a PGA depends on the configuration of Oracle.

163. WHAT IS AN ORACLE INSTANCE?
Ans: Every time a database is started, an SGA is allocated and Oracle
background processes are started. The combination of these processes and memory buffers is called an Oracle instance.

164. WHAT ARE DIFFERENT ORACLE PROCESSES?
Ans:  A process is a “thread of control” or a mechanism in an operating
system that can be execute a series of steps. Some operating systems use terms jobs or

task. A process normally has its own private memory area in which it runs. An Oracle database system has general types of process: User Processes and Oracle Processes.

**165. WHAT IS DIFFERENCE BETWEEN PMON AND SMON?
Ans: SMON (System Monitor) performs instance recovery at instance of
startup. In a multiple instance system (one that uses the parallel server), SMON of one instance can also perform instance recovery other instance that have failed whereas The PMON (Process Monitor) performs process recovery when a user process fails.

**166. WHAT IS DIFFERENCE BETWEEN DATABASE AND TABLESPACE?
Ans:  Database is a physical Component
          Tablespace is a Logical component

167. WHAT IS JOB OF DATABASE WRITER (DBWR) PROCESS?
Ans: The Data Base Writer writes modified blocks from the database
buffer cache to the data files.

168. WHAT IS JOB OF LOG WRITER (LGWR) PROC*SS?
Ans: The Log Writer writes redo log files to disk. Redo log data is
generated in the redo log buffer of the SGA. As transactions commit and log buffer fills, LGWR writes redo entries into an online redo log file.

169. WHAT IS RECOVERER?
Ans: The Recover (RECO) is used to resolve distributed transactions that are pending due to network or system failure in a distributed database. At timed intervals, the local RECO attempts to concept to remote database and automatically complete the commit or rollback of the local portion of any pending distributed transactions.

170. WHAT IS ARCHIVER?
Ans:  The Archiver (ARCH) copies the online redo log files to archival storage when they are full. ,ARCH is active only when a database’s redo log is used ARCHILOG mode.

** 171. WHAT IS A STORED QUERY?
Ans: VIEW

172. WHAT IS USER PROCESS AND SERVER PROCESS?
Ans: A User process is created and maintained to execute the software
code of an application program (such as PRO * Program) or an ORACLE tool (such as SQL * DBA). The User process also manages the communication
with server processes. User processes communication with the server
Processes through the program interface.

 Other processes call ORACLE processes. In a dedicated server
configuration, a server Process handles requests for a single user process. A multithread
server configuration allows many user processes to share a small number of server processes, minimizing the utilization of available system resources.

**173. WHAT IS A SELF REFERENTIAL INTEGRITY?
Ans: Table related to itself .Foreign key of the table links to primary  key of the same table.

174. WHAT IS A "RAISE" STATEMENT?
Ans: It is used to Raise Exceptions.

175. WHAT IS ROWID? HOW IT IS DIFFERENT FROM ROWNUM?
Ans: Rowid is the address of the row at where it is stored in the

database. Rownum is count of records whereas Rowid is identification of the each row.

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