Important Questions in Oracle, Developer

      Important Questions in Oracle, Developer /2000(Form 4.5 and Reports 2.5)
      Oracle :
      1) 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.

      2) 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

      3) 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.

      4) 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.
      h) 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.
      i) Redo log Buffer : Redo log Buffer of SGA stores all the redo log
      entries.
      j) 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.
      k) Process : A Process is a 'thread of control' or mechansim in Operating
      System that
      executes series of steps.

      5) 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 Provide a method of encapsulating and storing related procedures,
      functions, variables and other Package Contents

      6) 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.
      eg. 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.

      7) 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.

      8) 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.

      9) 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

      10) 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:
      set_item_property('DeptBlock',OPTIMIZER_HINT,'FIRST_ROWS');
      Select /*+ First_Rows */ Deptno,Dname,Loc,Rowid from dept where (Deptno >
      25)
      c) Optimize_Sql : By setting the Optimize_Sql = No, Oracle Forms assigns a
      single cursor for all SQL statements.This slow downs the processing
      because for evertime the SQL must be parsed whenver they are executed.
      f45run module = my_firstform userid = scott/tiger optimize_sql = No
      d) Optimize_Tp : By setting the Optimize_Tp= No, Oracle Forms assigns
      seperate cursor only for each query SELECT statement. All other SQL
      statements reuse the cursor.
      f45run module = my_firstform userid = scott/tiger optimize_Tp = No

      11) How do u implement the If statement in the Select Statement
      We can implement the if statement in the select statement by using the
      Decode statement.
      e.g select DECODE (EMP_CAT,'1','First','2','Second'Null);
      Here the Null is the else statement where null is done .

      12) How many types of Exceptions are there
      There are 2 types of exceptions. They are
      a) System Exceptions
      e.g. When no_data_found, When too_many_rows
      b) User Defined Exceptions
      e.g. My_exception exception
      When My_exception then

      13) What are the inline and the precompiler directives
      The inline and precompiler directives detect the values directly

      14) How do you use the same lov for 2 columns
      We can use the same lov for 2 columns by passing the return values in
      global values and using the global values in the code

      15) How many minimum groups are required for a matrix report
      The minimum number of groups in matrix report are 4

      16) What is the difference between static and dynamic lov
      The static lov contains the predetermined values while the dynamic lov
      contains values that come at run time

      17) 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

      18) 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 property classes as classes and the items as objects
      19) 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.

      20) 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.

      21) Previleges and Grants
      Previleges are the right to execute a particulare type of SQL statements.
      eg. 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.

      22) 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.

      23) 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
      24) 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
      25) 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 .

      26) 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
     
27) 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.
      
28) 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.
      
29) 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.

     
30) 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
     
31) 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.
      
32) Deleting the Duplicate rows in the table
      We can delete the duplicate rows in the table by using the Rowid
     
33) Can U disable database trigger? How?
      Yes. With respect to table
      ALTER TABLE TABLE
      [ DISABLE all_trigger ]
     
34) 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:
      * CURRVAL
      * NEXTVAL
      * LEVEL
      * ROWID
      * ROWNUM
     
35) How many columns can table have?
      The number of columns in a table can range from 1 to 254.
     


36) Is space acquired in blocks or extents ?
      In extents .
     
37) what is clustered index?
      In an indexed cluster, rows are stored together based on their cluster key
      values . Can not applied for HASH.

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

      39 ) What are attributes of cursor?
      %FOUND , %NOTFOUND , %ISOPEN,%ROWCOUNT

      40) Can you use select in FROM clause of SQL select ?
      Yes.