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.
1) This is one of the most frequently asked question. There are
basically 9 Processes but in a general system we need to mention the
first five background processes. They do the house keeping activities
for the Oracle and are common in any system.
The various background processes in oracle are
a) Data Base Writer(DBWR) :: Data Base Writer Writes Modified blocks
from Database buffer cache to Data Files. This is required since the
data is not written whenever a transaction is committed.
b)LogWriter(LGWR) :: LogWriter writes the redo log entries to disk.
Redo Log data is generated in redo log buffer of SGA. As transaction
commits and log buffer fills, LGWR writes log entries into a online
redo log file.
c) System Monitor(SMON) :: The System Monitor performs instance recovery
at instance startup.This is useful for recovery from system failure
d)Process Monitor(PMON) :: The Process Monitor performs process recovery
when user Process fails. Pmon Clears and Frees resources that process
were 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 storage 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
2) There are basically 6 types of sql statements.They are
a) Data Definition Language(DDL) :: The DDL statements define and
maintain objects and drop objects.
b) Data Manipulation Language(DML) :: The DML statements manipulate
database data.
c) Transaction Control Statements :: Manage change by DML
d) Session Control :: Used to control
the properties of current session enabling and disabling roles and
changing .e.g. :: Alter statements, Set Role
e) System Control Statements :: Change Properties of
Oracle Instance .e.g.:: Alter System
f) Embedded SQL :: Incorporate
DDL,DML and T.C.S in Programming Language. E.g.: Using the SQL
Statements in languages such as 'C', Open, Fetch, execute and close

3) What is a Transaction in Oracle?
3) A transaction is a logical unit of work that compromises one or more
SQL Statements executed by a single User. According to ANSI, a
transaction begins with first executable statement and ends when it
is explicitly committed or rolled back.

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

5) What are procedures ,functions and Packages ?
5) 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 value
Packages :: Packages Provide a method of encapsulating and storing
related procedures, functions, variables and other Package Contents

6) What are Database Triggers and Stored Procedures ?
6) 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 combinations
At statement 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
7) 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 Integrity 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.
8) The various Master and Detail Relationship are
a) NonIsolated :: The Master cannot be deleted when a child is existing.
b) Isolated :: The Master can be deleted when the child
is existing
c) Cascading :: The child gets deleted when the Master is deleted.

9) What are the Various Block Coordination Properties
9) 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 Optimization Techniques
10) The Various Optimization 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,'FIRS T_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
everytime the SQL must be parsed whenever 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
11) 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
12) There are 2 types of exceptions. They are
a) System Exceptions
e.g. When no_data_found, When too_many_rows, Dup_Val_on_index,
Value_Error,Others
b) User Defined Exceptions
e.g. My_exception exception
When My_exception then

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

14) How do you use the same lov for 2 columns
14) 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
15) The minimum number of groups in matrix report are 4

16) What is the difference between static and dynamic lov

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