Oracle  Placement Paper   Technical - Other   Not Specified-27 Nov 2008

Oracle  Placement Paper   Technical - Other   Not Specified-27 Nov 2008

  • Posted by  FreshersWorld 
    7 Jan, 2012


    1. There is a string 120000 12 0 .125 , how you will find the position of the decimal place?
    INSTR ('120000 12 0 .125',1,'.')
    output 13

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

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

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

    5. Difference between procedure and function.?
    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.

    6. Which is more faster - IN or EXISTS?
    EXISTS is more faster than IN because EXISTS returns a Boolean value whereas IN returns a value.

    7. What is syntax for dropping a procedure and a function .Are these operations possible?
    Drop Procedure procedure_name
    Drop Function function_name

    8. How will you delete duplicating rows from a base table?
    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);

    9. Difference between database triggers and Form triggers?
    -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.

    10. What is a cursor for loop?
    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.

    11. How you will avoid duplicating records in a query?
    By using DISTINCT

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

    13. What is difference between UNIQUE and PRIMARY KEY constraints?
    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.

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

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

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

    17. What are cursor attributes?

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

    19. What is ON DELETE CASCADE ?
    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.

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

    21. What is difference between TRUNCATE & DELETE ?
    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.

    22. What is a transaction ?
    Transaction is logical unit between two commits and commit and rollback.

    23. What are the advantages of VIEW ?
    To protect some of the columns of a table from other users.To hide complexity of a query.To hide complexity of calculations.

    24. How will you a activate/deactivate integrity constraints ?
    The integrity constraints can be enabled or disabled by ALTER TABLE ENABLE constraint/DISABLE constraint.

    25. Where the integrity constraints are stored in Data Dictionary ?
    The integrity constraints are stored in USER_CONSTRAINTS.

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

    27. 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 ?
    Sequence name CURRVAL, Sequence name NEXTVAL.It is not possible. Only if you access next value in the session, current value can be accessed

    28. What are the usage of SAVEPOINTS ?value in a session before accessing next value ?
    SAVE POINTS are used to subdivide a transaction into smaller parts. It enables rolling back part of a transaction. Maximum of five save points are allowed.

    29. What is ROWID ?in a session before accessing next value ?
    ROWID is a pseudo column attached to each row of a table. It is 18 character long, blockno, rownumber are the components of ROWID.

    30. Explain Connect by Prior ?in a session before accessing next value ?
    Retrieves rows in hierarchical order.e.g. select empno, ename from emp where.

    31. How many LONG columns are allowed in a table ? Is it possible to use LONG columns in WHERE clause or ORDER BY ?
    Only one LONG columns is allowed. It is not possible to use LONG column in WHERE or ORDER BY clause.

    32. What is Referential Integrity ?
    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.

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

    34. If an unique key constraint on DATE column is created, will it validate the rows that are inserted with SYSDATE ?
    It won't, Because SYSDATE format contains time attached with it.

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

    36. What is an Integrity Constraint ?
    Integrity constraint is a rule that restricts values to a column in a table.

    37. How does one create a repository? (for DBA
    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.

    38. If a View on a single base table is manipulated will the changes be reflected on the base table ?
    If changes are made to the tables which are base tables of a view will the changes be reference on the view.

    39. 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.

    40. What is a database link ?
    Database Link is a named path through which a remote database can be accessed.

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

    42. What is CYCLE/NO CYCLE in a Sequence ?
    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.

    43. What is correlated sub-query ?
    Correlated sub query is a sub query which has reference to the main query.

    44. What are the data types allowed in a table ?

    45 What is difference between CHAR and VARCHAR2 ? What is the maximum SIZE allowed for each type ?
    CHAR pads blank spaces to the maximum length. VARCHAR2 does not pad blank spaces. For CHAR it is 255 and 2000 for VARCHAR2.

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

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

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

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

    50. maxvalue.sql Select the Nth Highest value from a table?
    select level, max('col_name') from my_table where level = '&n' connect by prior ('col_name') > 'col_name')
    group by level;
    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

    51. Find out nth highest salary from emp table?
    For Eg:-
    Enter value for n: 2

    52. Suppose a customer table is having different columns like customer no, payments.What will be the query to select top three max payments?
    SELECT customer_no, payments from customer C1
    WHERE 3<=(SELECT COUNT(*) from customer C2
    WHERE C1.payment <= C2.payment)

    53. How you will avoid your query from using indexes?
    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

    54. What utility is used to create a physical backup?
    Either rman or alter tablespace begin backup will do..

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

    56. How many types of Sql Statements are there in Oracle
    There are basically 6 types of sql statments.They are
    a) Data Defination Language(DDL) :: The DDL statments define and maintain objects and drop objects.
    b) Data Manipulation Language(DML) :: The DML statments 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

    57. What is a Transaction in Oracle
    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 statment and ends when it is explicitly commited or rolled back.

    58. Key Words Used in Oracle
    The Key words that are used in Oracle are ::
    a) Commiting :: A transaction is said to be commited 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 transactino 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 stament. 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 Explcit 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 :: Databese Buffer of SGA stores the most recently used blocks of datatbase 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 mechansim in Operating System that executes series of steps.

    59. What are Procedure,functions and Packages
    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

    60. What are Database Triggers and Stored Procedures
    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.

    61. How many Integrity Rules are there and what are they
    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.

    62. What are the Various Master and Detail Relation ships.
    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.

    63. What are the Various Block Coordination Properties
    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

    64. What is in all those X$ tables? (for DBA
    The following list attempts to describe some x$ tables. The list may not be complete or accurate, but represents an attempt to figure out what information they contain. One should generally not write queries against these tables as they are internal to Oracle, and Oracle may change them without any prior notification.

    X$K2GTE2 Kernel 2 Phase Commit Global Transaction Entry Fixed Table
    X$K2GTE Kernel 2 Phase Commit Global Transaction Entry Fixed Table
    X$BH Buffer headers contain information describing the current contents of a piece of the buffer cache
    X$KCBCBH Cache Buffer Current Buffer Header Fixed Table. It can predict the potential loss of decreasing the number of database buffers. The db_block_lru_statistics parameter has to be set to true to gather information in this table.
    X$KCVFH File Header Fixed Table
    X$KDNCE SGA Cache Entry Fixed Table
    X$KDNST Sequence Cache Statistics Fixed Table
    X$KDXHS Histogram structure Fixed Table
    X$KDXST Statistics collection Fixed Table
    X$KGHLU One-row summary of LRU statistics for the shared pool
    X$KGLBODY Derived from X$KGLOB (col kglhdnsp = 2)
    X$KGLCLUSTER Derived from X$KGLOB (col kglhdnsp = 5)
    X$KGLINDEX Derived from X$KGLOB (col kglhdnsp = 4)
    X$KGLLC Latch Clean-up state for library cache objects Fixed Table
    X$KGLPN Library cache pin Fixed Table
    X$KGLTABLE Derived from X$KGLOB (col kglhdnsp = 1)
    X$KGLTR Library Cache Translation Table entry Fixed Table
    X$KGLTRIGGER Derived from X$KGLOB (col kglhdnsp = 3)
    X$KGLXS Library Cache Access Table
    X$KKMMD Fixed table to look at what databases are mounted and their status
    X$KKSBV Cursor Cache Bind Variables
    X$KSMSP Each row represents a piece of memory in the shared pool
    X$KSQDN Global database name
    X$KSQST Enqueue statistics by type
    X$KSUCF Cost function for each Kernel Profile (join to X$KSUPL)
    X$KSUPL Resource Limit for each Kernel Profile
    X$KSURU Resource Usage for each Kernel Profile (join with X$KSUPL)
    X$KSQST Gets and waits for different types of enqueues
    X$KTTVS Indicate tablespace that has valid save undo segments
    X$KVII Internal instance parameters set at instance initialization
    X$KVIS Oracle Data Block (size_t type) variables
    X$KVIT Instance internal flags, variables and parameters that can change during the life of an instance
    X$KXFPCDS Client Dequeue Statistics
    X$KXFPCMS Client Messages Statistics
    X$KZDOS Represent an os role as defined by the operating system
    X$KZSRO Security state Role: List of enabled roles
    X$LE Lock Element: each PCM lock that is used by the buffer cache (gc_db_locks)
    X$MESSAGES Displays all the different messages that can be sent to the Background processes
    X$NLS_PARAMETERS NLS database parameters

    Handy X$table queries
    Some handy queries based on the X$ memory tables:
    . Largest # blocks you can write at any given time:
    select kviival write_batch_size
    from x$kvii where kviitag = 'kcbswc';
    . See the gets and waits for different types of enqueues:
    select * from x$ksqst
    where ksqstget > 0;
    Oracle Kernel Subsystems
    Listed below are some of the important subsystems in the Oracle kernel. This table might help you to read those dreaded trace files and internal messages. For example, if you see messages like this, you will at least know where they come from: OPIRIP: Uncaught error 447. Error stack:
    KCF: write/open error block=0x3e800 online=1

    OPI Oracle Program Interface
    KK Compilation Layer - Parse SQL, compile PL/SQL
    KX Execution Layer - Bind and execute SQL and PL/SQL
    K2 Distributed Execution Layer - 2PC handling
    NPI Network Program Interface
    KZ Security Layer - Validate privs
    KQ Query Layer
    RPI Recursive Program Interface
    KA Access Layer
    KD Data Layer
    KT Transaction Layer
    KC Cache Layer
    KS Services Layer
    KJ Lock Manager Layer
    KG Generic Layer
    KV Kernel Variables (eg. x$KVIS and X$KVII)
    S or ODS Operating System Dependencies

    65. What are the Different Optimisation Techniques
    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 ::
    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

    66. How does one change an Oracle user's password? (for DBA
    Issue the following SQL command:
    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:

    67. How does one create and drop database users?
    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 DBA TO scott; -- Make user a DB Administrator
    Remember to give the user some space quota on its tablespaces:

    68. Who created all these users in my database?/ Can I drop this user? (for DBA
    Oracle creates a number of default database users or schemas when a new database is created. Below are a few of them:
    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
    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
    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
    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
    Oracle interMedia (ConText Cartridge) administrator user
    Created by: ?/ctx/admin/dr0csys.sql
    Oracle Trace server
    Created by: ?/rdbms/admin/otrcsvr.sql
    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
    Object Relational Data (ORD) User used by Time Series, etc.
    Created by: ?/ord/admin/ordinst.sql
    Object Relational Data (ORD) User used by Time Series, etc
    Created by: ?/ord/admin/ordinst.sql
    Oracle Dynamic Services and Syndication Server
    Created by: ?/ds/sql/dssys_init.sql
    Oracle Spatial administrator user
    Created by: ?/ord/admin/ordinst.sql
    Used for users who do not authenticate in Aurora/ORB
    Created by: ?/javavm/install/init_orb.sql called from ?/javavm/install/initjvm.sql
    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.

    69. How does one enforce strict password control? (for DBA
    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:
    ALTER USER scott PROFILE my_profile;

    70. How does one switch to another user in Oracle? (for DBA
    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';
    SQL> alter user scott identified by lion;
    User altered.

    SQL> connect scott/lion

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

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

    72. What are snap shots and views
    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

    73. What are the OOPS concepts in Oracle.
    Oracle does implement the OOPS concepts. The best example is the Property Classes. We can categorise 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 peroperty classes as classes and the items as objects

    74. What is the difference between candidate key, unique key and primary key
    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.)

    75. What is concurrency
    Cuncurrency 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.

    76. Previleges and Grants
    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.

    77. Table Space,Data Files,Parameter File, Control Files
    Table Space :: The table space is useful for storing the data in the database.When a database is created two table spaces are created.
    a) System Table space :: This data file stores all the tables related to the system and dba tables
    b) User Table space :: This data file stores all the user related tables
    We should have seperate table spaces for storing the tables and indexes so that the access is fast.
    Data Files :: Every Oracle Data Base has one or more physical data files.They store the data for the database.Every datafile is associated with only one database.Once the Data file is created the size cannot change.To increase the size of the database to store more data we have to add data file.
    Parameter Files :: Parameter file is needed to start an instance.A parameter file contains the list of instance configuration parameters e.g.::
    db_block_buffers = 500
    db_name = ORA7
    db_domain = u.s.acme lang
    Control Files :: Control files record the physical structure of the data files and redo log files
    They contain the Db name, name and location of dbs, data files ,redo log files and time stamp.

    78. Physical Storage of the Data
    The finest level of granularity of the data base are the data blocks.
    Data Block :: One Data Block correspond to specific number of physical database space
    Extent :: Extent is the number of specific number of contigious data blocks.
    Segments :: Set of Extents allocated for Extents. There are three types of Segments
    a) Data Segment :: Non Clustered Table has data segment data of every table is stored in cluster data segment
    b) Index Segment :: Each Index has index segment that stores data
    c) Roll Back Segment :: Temporarily store 'undo' information

    79. What are the Pct Free and Pct Used
    Pct Free is used to denote the percentage of the free space that is to be left when creating a table. Similarly Pct Used is used to denote the percentage of the used space that is to be used when creating a table
    eg.:: Pctfree 20, Pctused 40

    80. What is Row Chaining
    The data of a row in a table may not be able to fit the same data block.Data for row is stored in a chain of data blocks .

    81. What is a 2 Phase Commit
    Two Phase commit is used in distributed data base systems. This is useful to maintain the integrity of the database so that all the users see the same values. It contains DML statements or Remote Procedural calls that reference a remote object. There are basically 2 phases in a 2 phase commit.
    a) Prepare Phase :: Global coordinator asks participants to prepare
    b) Commit Phase :: Commit all participants to coordinator to Prepared, Read only or abort Reply

    82. What is the difference between deleting and truncating of tables
    Deleting a table will not remove the rows from the table but entry is there in the database dictionary and it can be retrieved But truncating a table deletes it completely and it cannot be retrieved.

    83. What are mutating tables
    When a table is in state of transition it is said to be mutating. eg :: If a row has been deleted then the table is said to be mutating and no operations can be done on the table except select.

    84. What are Codd Rules
    Codd Rules describe the ideal nature of a RDBMS. No RDBMS satisfies all the 12 codd rules and Oracle Satisfies 11 of the 12 rules and is the only Rdbms to satisfy the maximum number of rules.

    85. What is Normalisation
    Normalisation is the process of organising the tables to remove the redundancy.There are mainly 5 Normalisation rules.
    a) 1 Normal Form :: A table is said to be in 1st Normal Form when the attributes are atomic
    b) 2 Normal Form :: A table is said to be in 2nd Normal Form when all the candidate keys are dependant on the primary key
    c) 3rd Normal Form :: A table is said to be third Normal form when it is not dependant transitively

    86. What is the Difference between a post query and a pre query
    A post query will fire for every row that is fetched but the pre query will fire only once.

    87. Deleting the Duplicate rows in the table
    We can delete the duplicate rows in the table by using the Rowid

    88. Can U disable database trigger? How?
    Yes. With respect to table
    [[ DISABLE all_trigger ]]

    89. What is pseudo columns ? Name them?
    A pseudocolumn behaves like a table column, but is not actually stored in the table. You can select from pseudocolumns, but you cannot insert, update, or delete their values. This section describes these pseudocolumns:
    * LEVEL
    * ROWID
    * ROWNUM

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

    91. What is difference between UNIQUE and PRIMARY KEY constraints?
    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.

    92. How many columns can table have?
    The number of columns in a table can range from 1 to 254.

    93. Is space acquired in blocks or extents ?
    In extents .

    94. what is clustered index?
    In an indexed cluster, rows are stored together based on their cluster key values . Can not applied for HASH.

    95. what are the datatypes supported By oracle (INTERNAL)?
    Varchar2, Number,Char , MLSLABEL.

    96. What are attributes of cursor?

    97. Can you use select in FROM clause of SQL select ?

    98. Which trigger are created when master -detail rela?
    master delete property
    * NON-ISOLATED (default)
    a) on check delete master
    b) on clear details
    c) on populate details
    a) on clear details
    b) on populate details
    a) per-delete
    b) on clear details
    c) on populate details

    99. which system variables can be set by users?

    100. What are object group?
    An object group is a container for a group of objects. You define an object group when you want to package related objects so you can copy or reference them in another module.

    101. What are referenced objects?
    Referencing allows you to create objects that inherit their functionality and appearance from other objects. Referencing an object is similar to copying an object, except that the resulting reference object maintains a link to its source object. A reference object automatically inherits any changes that have been made to the source object when you open or regenerate the module that contains the reference object.

    102. Can you store objects in library?
    Referencing allows you to create objects that inherit their functionality and appearance from other objects. Referencing an object is similar to copying an object, except that the resulting reference object maintains a link to its source object. A reference object automatically inherits any changes that have been made to the source object when you open or regenerate the module that contains the reference object.

    104. Is forms 4.5 object oriented tool ? why?
    yes , partially. 1) PROPERTY CLASS - inheritance property 2) OVERLOADING : procedures and functions.

    105. Can you issue DDL in forms?
    yes, but you have to use FORMS_DDL.
    Referencing allows you to create objects that inherit their functionality and appearance from other objects. Referencing an object is similar to copying an object, except that the resulting reference object maintains a link to its source object. A reference object automatically inherits any changes that have been made to the source object when you open or regenerate the module that contains the reference object. Any string expression up to 32K:
    - a literal
    - an expression or a variable representing the text of a block of dynamically created PL/SQL code
    - a DML statement or
    - a DDL statement
    The statement you pass to FORMS_DDL may not contain bind variable references in the string, but the values of bind variables can be concatenated into the string before passing the result to FORMS_DDL

    106. What is SECURE property?
    - Hides characters that the operator types into the text item. This setting is typically used for password protection.

    107. What are the types of triggers and how the sequence of firing in text item
    Triggers can be classified as Key Triggers, Mouse Triggers ,Navigational Triggers.
    Key Triggers :: Key Triggers are fired as a result of Key action.e.g :: Key-next-field, Key-up,Key-Down
    Mouse Triggers :: Mouse Triggers are fired as a result of the mouse navigation.e.g. When-mouse-button-presed,when-mouse-doubleclicked,etc
    Navigational Triggers :: These Triggers are fired as a result of Navigation. E.g : Post-Text-item,Pre-text-item.
    We also have event triggers like when ?new-form-instance and when-new-block-instance.
    We cannot call restricted procedures like go_to(?my_block.first_item?) in the Navigational triggers
    But can use them in the Key-next-item.
    The Difference between Key-next and Post-Text is an very important question. The key-next is fired as a result of the key action while the post text is fired as a result of the mouse movement. Key next will not fire unless there is a key event. The sequence of firing in a text item are as follows ::
    a) pre - text
    b) when new item
    c) key-next
    d) when validate
    e) post text

    108. Can you store pictures in database? How?
    Yes , in long Raw datatype.

    109. What are property classes ? Can property classes have trigger?
    Property class inheritance is a powerful feature that allows you to quickly define objects that conform to your own interface and functionality standards. Property classes also allow you to make global changes to applications quickly. By simply changing the definition of a property class, you can change the definition of all objects that inherit properties from that class.
    Yes . All type of triggers .

    110. If you have property class attached to an item and you have same trigger written for the item . Which will fire first?
    Item level trigger fires , If item level trigger fires, property level trigger won't fire. Triggers at the lowest level are always given the first preference. The item level trigger fires first and then the block and then the Form level trigger.

    111. What are record groups ? Can record groups created at run-time?
    A record group is an internal Oracle Forms data structure that has a column/row framework similar to a database table. However, unlike database tables, record groups are separate objects that belong to the form module in which they are defined. A record group can have an unlimited number of columns of type CHAR, LONG, NUMBER, or DATE provided that the total number of columns does not exceed 64K. Record group column names cannot exceed 30 characters.
    Programmatically, record groups can be used whenever the functionality offered by a two-dimensional array of multiple data types is desirable.
    Query Record Group A query record group is a record group that has an associated SELECT statement. The columns in a query record group derive their default names, data types, and lengths from the database columns referenced in the SELECT statement. The records in a query record group are the rows retrieved by the query associated with that record group.
    Non-query Record Group A non-query record group is a group that does not have an associated query, but whose structure and values can be modified programmatically at runtime.
    Static Record Group A static record group is not associated with a query; rather, you define its structure and row values at design time, and they remain fixed at runtime.

    112. What are ALERT?
    An ALERT is a modal window that displays a message notifiying operator of some application condition.

    113. Can a button have icon and lable at the same time ?

    114. What is mouse navigate property of button?
    When Mouse Navigate is True (the default), Oracle Forms performs standard navigation to move the focus to the item when the operator activates the item with the mouse.
    When Mouse Navigate is set to False, Oracle Forms does not perform navigation (and the resulting validation) to move to the item when an operator activates the item with the mouse.

    115. What is FORMS_MDI_WINDOW?
    forms run inside the MDI application window. This property is useful for calling a form from another one.

    116. What are timers ? when when-timer-expired does not fire?
    The When-Timer-Expired trigger can not fire during trigger, navigation, or transaction processing.

    117. Can object group have a block?
    Yes , object group can have block as well as program units.

    118. How many types of canvases are there.
    There are 2 types of canvases called as Content and Stack Canvas. Content canvas is the default and the one that is used mostly for giving the base effect. Its like a plate on which we add items and stacked canvas is used for giving 3 dimensional effect.

    119. What are user-exits?
    It invokes 3GL programs.

    120. Can you pass values to-and-fro from foreign function ? how ?
    Yes . You obtain a return value from a foreign function by assigning the return value to an Oracle Forms variable or item. Make sure that the Oracle Forms variable or item is the same data type as the return value from the foreign function.
    After assigning an Oracle Forms variable or item value to a PL/SQL variable, pass the PL/SQL variable as a parameter value in the PL/SQL interface of the foreign function. The PL/SQL variable that is passed as a parameter must be a valid PL/SQL data type; it must also be the appropriate parameter type as defined in the PL/SQL interface.

    121. What is IAPXTB structure ?
    The entries of Pro * C and user exits and the form which simulate the proc or user_exit are stored in IAPXTB table in d/b.

    122. Can you call WIN-SDK thruo' user exits?

    123. Does user exits supports DLL on MSWINDOWS ?
    YES .

    124. What is path setting for DLL?
    Make sure you include the name of the DLL in the FORMS45_USEREXIT variable of the ORACLE.INI file, or rename the DLL to F45XTB.DLL. If you rename the DLL to F45XTB.DLL, replace the existing F45XTB.DLL in the ORAWINBIN directory with the new F45XTB.DLL.

    125. How is mapping of name of DLL and function done?
    The dll can be created using the Visual C++ / Visual Basic Tools and then the dll is put in the path that is defined the registery.

    126. what is precompiler?
    It is similar to C precompiler directives.

    127. Can you connect to non - oracle datasource ? How?
    Yes .

    128. What are key-mode and locking mode properties? level ?
    Key Mode : Specifies how oracle forms uniquely identifies rows in the database.This is property includes for application that will run against NON-ORACLE datasources .
    Key setting unique (default.)

    Locking mode :
    Specifies when Oracle Forms should attempt to obtain database locks on rows that correspond to queried records in the form. a) immediate b) delayed

    129. What are savepoint mode and cursor mode properties ? level?
    Specifies whether Oracle Forms should issue savepoints during a session. This property is included primarily for applications that will run against non-ORACLE data sources. For applications that will run against ORACLE, use the default setting.
    Cursor mode - define cursur state across transaction Open/close.

    130. What is transactional trigger property?
    Identifies a block as transactional control block. i.e. non - database block that oracle forms should manage as transactional block.(NON-ORACLE datasource) default - FALSE.

    131. What is OLE automation ?
    OLE automation allows an OLE server application to expose a set of commands and functions that can be invoked from an OLE container application. OLE automation provides a way for an OLE container application to use the features of an OLE server application to manipulate an OLE object from the OLE container environment. (FORMS_OLE)

    132. What does invoke built-in do?
    This procedure invokes a method.
    (object obj_type,
    method VARCHAR2,
    list list_type := 0);
    object Is an OLE2 Automation Object.
    method Is a method (procedure) of the OLE2 object.
    list Is the name of an argument list assigned to the OLE2.CREATE_ARGLIST function.

    133. What are OPEN_FORM,CALL_FORM,NEW_FORM? diff?
    CALL_FORM : It calls the other form. but parent remains active, when called form completes the operation , it releases lock and control goes back to the calling form.
    When you call a form, Oracle Forms issues a savepoint for the called form. If the CLEAR_FORM function causes a rollback when the called form is current, Oracle Forms rolls back uncommitted changes to this savepoint.
    OPEN_FORM : When you call a form, Oracle Forms issues a savepoint for the called form. If the CLEAR_FORM function causes a rollback when the called form is current, Oracle Forms rolls back uncommitted changes to this savepoint.
    NEW_FORM : Exits the current form and enters the indicated form. The calling form is terminated as the parent form. If the calling form had been called by a higher form, Oracle Forms keeps the higher call active and treats it as a call to the new form. Oracle Forms releases memory (such as database cursors) that the terminated form was using.
    Oracle Forms runs the new form with the same Runform options as the parent form. If the parent form was a called form, Oracle Forms runs the new form with the same options as the parent form.

    134. What is call form stack?
    When successive forms are loaded via the CALL_FORM procedure, the resulting module hierarchy is known as the call form stack.

    135. Can u port applictions across the platforms? how?
    Yes we can port applications across platforms.Consider the form developed in a windows system.The form would be generated in unix system by using f45gen my_form.fmb scott/tiger

    136. What is a visual attribute?
    Visual attributes are the font, color, and pattern properties that you set for form and menu objects that appear in your application's interface.

    137. Diff. between VAT and Property Class? imp
    Named visual attributes define only font, color, and pattern attributes; property classes can contain these and any other properties.
    You can change the appearance of objects at runtime by changing the named visual attribute programmatically; property class assignment cannot be changed programmatically. When an object is inheriting from both a property class and a named visual attribute, the named visual attribute settings take precedence, and any visual attribute properties in the class are ignored.

    138. Which trigger related to mouse?

    138. What is Current record attribute property?
    Specifies the named visual attribute used when an item is part of the current record. Current Record Attribute is frequently used at the block level to display the current row in a multi-record If you define an item-level Current Record Attribute, you can display a pre-determined item in a special color when it is part of the current record, but you cannot dynamically highlight the current item, as the input focus changes.

    139. Can you change VAT at run time?
    Yes. You can programmatically change an object's named visual attribute setting to change the font, color, and pattern of the object at runtime.

    140. Can you set default font in forms?
    Yes. Change windows registry (regedit). Set form45_font to the desired font.

    141. What is Log Switch ?
    The point at which ORACLE ends writing to one online redo log file and begins writing to another is called a log switch.

    142. What is On-line Redo Log?
    The On-line Redo Log is a set of tow or more on-line redo files that record all committed changes made to the database. Whenever a transaction is committed, the corresponding redo entries temporarily stores in redo log buffers of the SGA are written to an on-line redo log file by the background process LGWR. The on-line redo log files are used in cyclical fashion.

    143. Which parameter specified in the DEFAULT STORAGE clause of CREATE TABLESPACE cannot be altered after creating the tablespace?
    All the default storage parameters defined for the tablespace can be changed using the ALTER TABLESPACE command. When objects are created their INITIAL and MINEXTENS values cannot be changed.

    144. What are the steps involved in Database Startup ?
    Start an instance, Mount the Database and Open the Database.

    145. What are the steps involved in Instance Recovery ?
    Rolling forward to recover data that has not been recorded in data files, yet has been recorded in the on-line redo log, including the contents of rollback segments. Rolling back transactions that have been explicitly rolled back or have not been committed as indicated by the rollback segments regenerated in step a. Releasing any resources (locks) held by transactions in process at the time of the failure. Resolving any pending distributed transactions undergoing a two-phase commit at the time of the instance failure

    146. Can Full Backup be performed when the database is open ?

    147. What are the different modes of mounting a Database with the Parallel Server ?
    Exclusive Mode If the first instance that mounts a database does so in exclusive mode, only that Instance can mount the database.
    Parallel Mode If the first instance that mounts a database is started in parallel mode, other instances that are started in parallel mode can also mount the database.

    148. What are the advantages of operating a database in ARCHIVELOG mode over operating it in NO ARCHIVELOG mode ?
    Complete database recovery from disk failure is possible only in ARCHIVELOG mode. Online database backup is possible only in ARCHIVELOG mode.

    149. What are the steps involved in Database Shutdown ?
    Close the Database, Dismount the Database and Shutdown the Instance.

    150. What is Archived Redo Log ?
    Archived Redo Log consists of Redo Log files that have archived before being reused.

    151. What is Restricted Mode of Instance Startup ?
    An instance can be started in (or later altered to be in) restricted mode so that when the database is open connections are limited only to those whose user accounts have been granted the RESTRICTED SESSION system privilege.

    152. Can you have OLE objects in forms?

    153. Can you have VBX and OCX controls in forms ?

    154. What are the types of windows (Window style)?
    Specifies whether the window is a Document window or a Dialog window.

    155. What is OLE Activation style property?
    Specifies the event that will activate the OLE containing item.

    156. Can you change the mouse pointer ? How?
    Yes. Specifies the mouse cursor style. Use this property to dynamically change the shape of the cursor.

    157. How many types of columns are there and what are they
    Formula columns :: For doing mathematical calculations and returning one value Summary Columns :: For doing summary calculations such as summations etc. Place holder Columns :: These columns are useful for storing the value in a variable

    158. Can you have more than one layout in report?
    It is possible to have more than one layout in a report by using the additional layout option in the layout editor.

    159. Can you run the report with out a parameter form ?
    Yes it is possible to run the report without parameter form by setting the PARAM value to Null

    160. What is the lock option in reports layout?
    By using the lock option we cannot move the fields in the layout editor outside the frame. This is useful for maintaining the fields .

    161. What are the minimum number of groups required for a matrix report
    The minimum of groups required for a matrix report are 4 e -----

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

    163. What is a Sequence ?
    A sequence generates a serial list of unique numbers for numerical columns of a database's tables.

    164. What is a Segment ?
    A segment is a set of extents allocated for a certain logical structure.

    165. What is schema?
    A schema is collection of database objects of a User.

    166. Describe Referential Integrity ?
    A rule defined on a column (or set of columns) in one table that allows the insert or update of a row only if the value for the column or set of columns (the dependent value) matches a value in a column of a related table (the referenced value). It also specifies the type of data manipulation allowed on referenced data and the action to be performed on dependent data as a result of any action on referenced data.

    167.What is hash cluster?
    A row is stored in a hash cluster based on the result of applying a hash function to the row's cluster key value. All rows with the same hash key value are stores together on disk.

    168. What is a Private Synonyms ?
    A Private Synonyms can be accessed only by the owner.

    169. What is Database Link ?
    A database link is a named object that describes a "path" from one database to another.

    170. What is index cluster?
    A cluster with an index on the cluster key.

    171. When can hash cluster used?
    Hash clusters are better choice when a table is often queried with equality queries. For such queries the specified cluster key value is hashed. The resulting hash key value points directly to the area on disk that stores the specified rows.

    178. What are the types of database links?
    Private database link, public database link & network database link.

    179. What is private database link?
    Private database link is created on behalf of a specific user. A private database link can be used only when the owner of the link specifies a global object name in a SQL statement or in the definition of the owner's views or procedures.

    180. What is public database link?
    Public database link is created for the special user group PUBLIC. A public database link can be used when any user in the associated database specifies a global object name in a SQL statement or object definition.

    181. What is network database link?
    Network database link is created and managed by a network domain service. A network database link can be used when any user of any database in the network specifies a global object name in a SQL statement or object definition.

    182. What is data block?
    Oracle database's data is stored in data blocks. One data block corresponds to a specific number of bytes of physical database space on disk.

    183. 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 cannot be changed latter.

    184. What is row chaining?
    In circumstances, all of the data for a row in a table may not be able to fit in the same data block. When this occurs, the data for the row is stored in a chain of data block (one or more) reserved for that segment.

    185. 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.

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

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

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

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

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

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

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

    193. 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 table space.

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

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

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

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

    198. 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.

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