How to change UserID and Password in Oracle.

How to change UserID and Password in Oracle.
what are differenct types of joins. explain outer join.
How to print output in Oracle.
what is a data control component.
why do we use DBMS ?
what are logical objects in RDBMS (tables & views).
what do you know about IDL?
can we maintain mirror data in different databases.
Data Integrity constraint is
(a)to ensure the presence of primary key
What is indexing in databases?
What is atomicity?
What is DBMS and RDBMS ?
types of DBMS,queries
Difference between Unique and primary
what is a cursor
types of cursors
normalization
normal forms
whis is the best normal form
what is an os
what exactly os consists ?
Types of joins ?
what is a trigger ?
can we create a table in oracle which is not in first
normal form
difference between dbms and rdbms
sql queries
types of indexing
DML,DDL, SQL querry,primary key, whts a null
diff btw DDL,DML, whts parallel DML,
whts normalisation explain with example till 3NF
6>need for normalisation
differnce btw oracle 8.0,8i,9i
what are pseudocolumns? given example.
(CURRVAl,LEVEL,NEXTVAL,ROWID,ROWNUM)
what are synonyms ? example.
( an alias name to the table , which
location transperancy.)
is
used
for
CREATE SYNONYM emp2 FOR emp@newyork;
SELECT ename, job INTO my_ename, my_job
FROM emp2
WHERE empno = my_empno;
what are snapshots.
what is indexing. what are its advantages.
what is cluster. advantages.
how do you add primary key to the table already
existing.
what is table space.
what partitioning. how many types of partitions.
what is mutating table.
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.
what is the keyword type.
what is 'exists'.
what is a cursor. what are the types.
two types of cursors: implicit and
declares a cursor implicitly for all
explicit.
PL/SQL
SQL data manipulation statements, including queries that
return only one row. However,
for queries that return more than one row, you must
declare an explicit cursor or use
a cursor FOR loop.
three commands to control the cursor: OPEN,
CLOSE.
FETCH,
and
initialize the cursor with the OPEN statement, which
identifies the active set.
Then, you use the FETCH statement to retrieve the first
row.
You can execute FETCH repeatedly until all rows have been
retrieved.
release the cursor with the CLOSE statement.
DECLARE
CURSOR c1 IS SELECT ename FROM emp;
name1 emp.ename%TYPE;
name2 emp.ename%TYPE;
name3 emp.ename%TYPE;
BEGIN
OPEN c1;
FETCH c1 INTO name1; -- this fetches first row
FETCH c1 INTO name2; -- this fetches second row
FETCH c1 INTO name3; -- this fetches third row
...
CLOSE c1;
END;
four
attributes
of
%ROWCOUNT, and %ISOPEN
cursor
:
%NOTFOUND,
%FOUND,
what is SGA.
The SGA is a shared memory region allocated by the
Oracle that
contains Data and control information for one Oracle
Instance.
It consists
Buffer.
of
Database
Buffer
Cache
and
Redo
log
how do you override function/procedures in oracle.
what is raise_application_error.
what are datafiles.
what are the default table spaces.
what are the background processes in oracle.
what are control files.
what are the minimum privilege for the user to connect
database.
what is a role. why do you create it.
Software Engineering
~~~~~~~~~~~~~~~~~~~~
what is waterfall model, prototype model etc.
what is testing. what is unit testing, integration
testing etc.
what are the stages in software project.
(study,analysis,design,development,testing,implementatio
n)
what is done in each stage of the SDLC.
what is the output of analysis stage.
what is er-model.
how do you compare an entity with class or object.
how do you design a project.
Procedure of any model
testing procedure of software
Models-Spiral, Prototyping, Estimation models
Software Configuration Management process is Capability Maturity Model( 5 stages)
Flow chart details
Software Development Life Cycle
where is development ?
Why do we go for Testing ?
Types of Testing ?
Software Life Cycle ?
what is testing
Funtional point model
difference between black box and white box
what is quality and various quality certifications
what is spiral lifecycle model
Cohesion and coupling
ORACLE
Doubts :
•
•
•
•
•
•
WHAT R SYNONYMS AND SEQUENCES IN PL/SQL;
how can you store a image in the database.
what do you mean by where current of C1
LONG RAW data type is used for storing BLOB's (binary large objects).( ie graphics and
images)
what is soundex built in function
what is to_number, to_char.
Integrity : the quality or state of being complete; unbroken condition; wholeness; entirety .
Consistency : agreement, holding firmly.
Constrain : to force into, or hold in, close bounds
Introduction to Oracle
Oracle is a comprehensive operating environment that packs the power of mainframe
relation database management system into user’s micro computer. It provides a set of functional
programs that user can use as tools to build structures and perform tasks. Because applications are
developed on oracle are completely portable to the other versions of the programmer can create a
complex application in a single user, environment and them move it to a multi user platform.Users
do not have to be an expert to appriciate Oracle but the better user understand the program,the
more productively and creatively he can use the tools it provides
Relational Database Management system
A Relational Database Management System (RDBMS) can perform a wide
range of tasks. It acts as a transparent interface between the physical storage and the logical
presentation of data.It provides a set of more or less flexible and sofesticated tools for handling
information.
Users can use the tools to
• Define a Database
• Query the Database
• Add,Edit and Delete data.
• Modify the structure of the Database.
• Communicate with in the Networks.
• Exports and Imports the data.
• Security.
Oracle the Right Tool
To keep track of records is often the best reason to consider buying a
software package.Choosing a proven product increase the chance that we will get a system capable
of meeting all our needs .Oracle has had many years in the relational market to often on the
large,Complex applications. Although Oracle demands greater expertise on the part of the
application developed,an application developed oracle will be able to keep pace with growth and
change in the world at large.
Oracle Gives You Security and Control
Oracle has several features that ensure the integrity of the data base. If an interruption
occurs in processing, a Rollback can reset the database to a point before the disaster. If a restore is
necessary, Oracle has a Roll forward command for recreating your database to its mast resent save
point.
Oracle provides user with several functions for securing data. Grant and Revoke
commands limit access to information down to the row and column levels. Views are valuable
feature for limiting access to the primary tables in the database.
The Oracle Environment
Oracle is a modular system that consists of the Oracle database and several functional
programs. Oracle’s tools do four major things of work.
1. Database Management.
2. Data access and Manipulation.
3. Programming
4. Connectivity.
Database Management Tools
This (is usually known as RDBMS by oracle) includes the core programs for Oracle’s
database management system, the Oracle database with its associated tables and views, which are
stores information related to every fact of the database system.User name, user access rights, table
attribute, storage information and auditing data for disaster recovery are stored in the data
dictionary.
The Database Administrator
The person responsible for a Database is called the DatabaseAdministrator(DBA).The
DBA has a special set of previleges and has complete over the database.Any system with more
than one user should have a DBA.The function of DBA include.
Creating primary database storage structures.
Modifying the structure of the database.
Backing up and restoring the database.
Monitoring database performance and efficiency.
Transfering data between database and external files.
Manipulating the phisical location of the database.
THE END USER
End user have less complex but equally important tasks.They must be able to
• Query the database.
• Generate printed output.
• Share data with or secure data from others.
• Use non-export methods to update the database.
• Define applications from a user point of view.
WHY ORACLE ?
Oracle is an open system i.e. the database is accessing by different data access
languages like SQL, Visual Basic, Power Builders,Delphi,VC++,JAVA etc.
Oracle supports database upto gigabytes in size.
* Oracle supports large number of concurrent users.
* Oracle supports true client/server environment.if enable processing to be spilt between
database server and the client application programs.
* Oracle provides high levelof data security in terms of users, passwords privileges, and
permissions.
* Oracle database behaves same on all platform line Windows,Unix,Dos,Mainframes etc.
Structure of Oracle Database:
physical structure:
one or more data files, Two of more log files, One control file.
Logical structure:
Table spaces,
Segments, Extents, Data blocks.
The data files contain all user data in terms of tables, index, and views. The log files
contain the information to open and be recovered, of Undone after a transaction(Rollback).
The control file physical data, media information to open and manage data files .If the
control file is damaged the server will not be able to open are use the database even if the
database is undamaged.
What are the Back ground processes in Oracle and what are they. ?
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.
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.
NORMALIZATION
Normalization is a process of simplifying the relationship between data elements in a
record. Through Normalization a collection of data in a record structure is replaced by successive
record structures that are simpler and more predictable and therefore more manageable. It is
process of reducing redundancy and eliminating the anomalies. (anamali means inconsistent state.)
Normalization is carried out for four reasons:
• To Structure the data so that any pertinent relationships between entities can be
represented.
• To permit simple retrieval of data in response to query and report requests.
• To simplify the maintenance of the data through updates, insertions, and deletion
• To reduce the need to restructure or reorganize data when new application requirements
arise.
• Normalization can improve the quality of design for an application.
There are totally Five Normal Forms(Rules) out of which, any database should necessarily satisfy
three of them, those Three Normal Forms are as follows:
First normal form is achieved when all repeating groups are removed so that a record is
of fixed length. A repeating group, the re-occurrence of a data item within a record, is actually
another relation. Hence, it is removed from the record and treated as an additional record structure,
or relation.
Second Normal form should be in first normal form and no partial dependency exists.
Means if we have a composite primary key(combination of 2 or more fields) then all the non keys
must depend on the composite primary key. no attribute should depend upon the part of key.(for
example if Rollno and SSno is a composite key, then no other field in that particular table should
be depedent upon either Rollno or ssno individually)
Third Normal form is achieved when Transitive Dependencies are removed from a record
design.
The general case is as follows :
A,B and C are three data items in a record. If C is functionally dependent on B (2nd N.F) and
B is functionally dependent on A Then C is functionally dependent on A Therefore, a Transitive
Dependency exists.
In data management, transitive dependency is a concern because data can inadvertently be
lost when the relationship is hidden. In the general case above, if A is deleted, then B and C are
deleted also, whether or not this is intended. This problem is eliminated by designing the record
for third normal form. Conversion to third normal form removes the transitive dependency by
splitting the relation into two separate relations.
BCNF must be 3NF and every determinant is a candidate key. Candidate key is other than
primary key, which uniquely identify each row in the table.
for example ssno is PK then rollno becomes Candidate key.
4NF and 5NF are depends on instance. we can not give a proper def.
bcz it all depends on joins.
“CODD’s 12 RULES" for a fully Relational DBMS
INTRODUCTION
According to Elmasri and Navathe (1994), Dr. E. F. Codd, the originator of the relational
data model, published a two-part article in ComputerWorld (Codd, 1985) that lists 12 rules for
how to determine whether a DBMS is relational and to what extent it is relational. These rules
provide a very useful yardstick for evaluating a relational system. Codd also mentions that,
according to these rules, no fully relational system is available yet. In particular, rules 6, 9, 10, 11,
and 12 are difficult to satisfy.
THE 12 RULES
Rule 1: The Information Rule
All information in a relational database is represented explicitly at the logical level in
exactly one way by values in tables.
All data is represented in the form of relations/tables (with rows and columns)Simple
Consistent and versatile
Rule 2: Guaranteed Access Rule
Each and every datum (atomic value) in a relational database is guaranteed to be logically
accessible by resorting to a table name, primary key value, and column name. All Data is uniquely
identified and accessible via this identity.
Rule 3: Systematic Treatment of Null Values
Null values (distinct from empty character string or a string of blank characters and distinct
from zero or any other number) are supported in the fully relational DBMS for representing
missing information in a systematic way, independent of data type.
Rule 4: Dynamic On-line Catalog based on the Relational Model
The database description is represented at the logical level in the same way as ordinary
data, so authorized users can apply the same relational language to its interrogation as they apply
to regular data.
Rule 5: Comprehensive Data Sublanguage Rule
A relational system may support several languages and various modes of terminal use (for
example, the fill-in-blanks mode). However, there must be at least one language whose statements
are expressible, per some well-defined syntax, as character strings and whose ability to support all
of the following is comprehensible: data definition, view definition, data manipulation (interactive
and by program), integrity constraints, and transaction boundaries (begin, commit, and rollback).
Rule 6: View Updating Rule
All views that are theoretically updateable are also updateable by the system.
Views are virtual tables. They appear to behave as conventional tables except that they are built
dynamically when the query is run. This means that a view is always up to date. It is not always
theoretically possible to update views. One problem exists when a view relates to part of a table
not including a candidate key. This means that potential updates would violate the entity integrity
rule.
Rule 7: High-level Insert, Update, and Delete
The capability of handling a base relation or a derived relation as a single operand applies
not only to the retrieval of data but also to the insertion, update, and deletion of data. i.e. The user
should be allowed to Delete, Update a set of tuples (rather than row by row)
Rule 8: Physical Data Independence
Application programs and terminal activities remain logically unimpaired whenever any
changes are made in either storage representation or access methods. i.e. Users and programs are
not dependent on the physical structure of the database.
Rule 9: Logical Data Independence
Application programs and terminal activities remain logically unimpaired when
information-preserving changes of any kind that theoretically permit unimpairment are made to
the base tables. Users and Programs are independent of the logical structure of the database, i.e.
the logical structure of the data can evolve with minimal impact on the programs.
Rule 10: Integrity Independence
Integrity constraints specific to a particular relational database must be definable in the
relational data sublanguage and storable in the catalog, not in the application programs. A
minimum of the following two integrity constraints must be supported:
1. Entity integrity: No component of a primary key is allowed to have a null value.
2. Referential integrity: For each distinct non-null foreign key value in a relational database,
there must exist a matching primary key value from the same domain.
Rule 11: Distribution Independence
A relational DBMS has distribution independence. Distribution independence implies that
users should not have to be aware of whether a database is distributed. Applications should still
work in a distributed database (DDB).
Rule 12: Nonsubversion Rule
If a relational system has a low-level (single-record-at-a-time) language, that low-level
language cannot be used to subvert or bypass the integrity rules or constraints expressed in the
higher-level (multiple-records-at-a-time) relational language.
If there is a record at a time interface (e.g. via 3GL), Security and integrity of the database
must no be violated. There should be no backdoor to bypass the security imposed by the DBMS.
On the basis of the above rules, there is no fully relational DBMS available today.
Questions and Answers :
What is Pseudo Colomn ?
USER, UID, SYSDATE, ROWNUM, ROWID, NULL, AND LEVEL
How to Display output in PL/SQL ?
we first set serveroutput on at SQL Prompt. and then in sql programming we specify as
dbms_output.put_line(‘hdjhd’ || ‘sakdha’);
No Displays are allowed in PL/SQL programming with select statement
Write about Commands and Keywords ?
Alter : ALTER TABLE EMP ADD ………. , MODIFY ………. ;
for a in 1..10
loop
………..
end loop;
loop exit when a<1 ……………… end loop;
while ….. loop……………..end loop;
Data Types : number, integer, varchar2, char, date, Boolean;
goto procedure name;…………..<<procedure name>>…………..
exit, rollback, commit, savepoint.
References: This keyword is used to refer two similar fields of different tables.
What are different built in functions ?
CONCATENATE, INITCAP, LENGTH, LOWER, UPPER, LPAD, RPAD, LTRIM
(removes the character specified left side of word), RTRIM, SUBSTR (displays values from
specified location onwards), TRANSLATE (for single character), REPLACE (for more than one
character ),CHR ( prints character of given ASCII value), ASCII (value of given character ).
ABS, CEIL, FLOOR, SQRT, POWER, SIGN, TRUNC, ROUND, EXP, MOD, LOG, LN,
GREATEST, LEAST, SYSDATE, ADD_MONTHS, MONTHS_BETWEEN.
what are emp.sal%type and emp%rowtype ?
First one is to assign a variable of type sal only.
Second is to assign a complete row of type emp table.
What are constraints ?
Constraint Clause : This will constrain a single column or a group of columns in a table.
and are used for maintaining integrity of the database.
Different Constraints are : candidate keys, primary keys, foreign keys, check conditions.
Can specify as a part of column definition, or at the end of the table (if more than one column).
Check Constraint : for validations to fields.
Naming Constraint (table constraints): Can name the constraint else system will name it
by default.
Different types of joins ?
Equi join : where emp.deptno = dept.deptno;
Non Equi join : where e.sal >= g.losal;
Outer join :***********e.deptno(+)=d.deptno;
Different types of Keys ?
Foreign Key : This is a referential integrity constraint and specifies the values of primary
key in other table. and is mentioned as :
DEPTNO number(2) REFERENCES DEPT(DEPTNO);
The clause ON DELETE CASCADE added to REFERENCES clause tells Oracle to delete the
dependent rows when we delete the row in the parent table.
Unique Key : If declared, then does not accept duplicate and also NULL values. And can
have many Unique key fields.
Primary Key : Similar to Unique key but, also maintains an index on primary key and also
used to connect two tables.
Write about cursors ?
Implicit (SQL is implicit by default ) and Explicit cursors.
EXIT WHEN C1%NOTFOUND, IF C1%FOUND THEN, IF C1%ISOPEN THEN,
FOR LOOP in CURSOR will :
1) open the cursor.
2) fetches the records from cursor one by one.
3) keeps the track of number of records in the cursor.
Super Dynamism in Cursors is obtained by passing the values as parameters( ie pass by value)
ie., for x in c1(a,b)
Multiple Cursors : These are nothing but nested cursors………..
In Implicit Cursors there is no need of declaration of cursors, by default system will create
a cursor whenever a query is written…and the conditions are like if SQL%NOTFOUND
if SQL%ROWCOUNT > 2 will keep a count of the number of records updated.
SQL is a keyword and cannot be used to name as a cursor name explicitly.
Difference between group functions and single row functions ?
Group Function
Single Row Function
A group function operates
A single row function
on many rows returns one and
result for one row.
returns single result.
Not allowed in Pl/sql procedural
Allowed in Pl/Sql Procedural statements
eg SUM(),AVG,MIN,MAX etc
eg UPPER,LOWER,CHR...
Difference between DECODE and TRANSLATE ?
DECODE is value by value
TRANSLATE is character by
character replacement.
replacement.
Ex SELECT DECODE('ABC','A',1,'B',2,'ABC',3) eg SELECT
from dual; o/p 3
TRANSLATE('ABCGH',
'ABCDEFGHIJ', 1234567899)
FROM DUAL; o/p 12378
(DECODE command is used to bring IF,THEN,ELSE logic to SQL.It tests for the IF values(s) and
then aplies THEN value(s) when true, the ELSE value(s) if not.)
Difference between TRUNCATE and DELETE ?
TRUNCATE deletes much faster than DELETE
Truncate
It is a DDL statement
It is a one way trip,cannot
ROLLBACK
Doesn't have selective features (where clause)
Doesn't fire database triggers
It requires disabling of referential
constraints.
Delete
It is a DML statement
One can Rollback
Has
Does
Does not require
What is a CO-RELATED SUBQUERY ?
A CO-RELATED SUBQUERY is one that has a correlation name as table or view designator in
the FROM clause of the outer query and the same correlation name as a qualifier of a search
condition in the WHERE clause of the subquery.
SELECT field1 from table1 X WHERE field2>(select avg(field2) from table1 Y
eg
where field1=X.field1);
(The subquery in a correlated subquery is revaluated
for every row of the table or view named in the outer query.)
What are various joins used while writing SUBQUERIES ?
Self join-Its a join foreign key of a table references the same table.
Outer Join--Its a join condition used where One can query all the rows of one of the
tables in the join condition even though they don't satisfy the join condition.
Equi-join--Its a join condition that retrieves rows from one or more tables in which one
or more columns in one table are equal to one or more columns in the second table.
What are various constraints used in SQL ?
NULL, NOT NULL, CHECK, DEFAULT
What are different Oracle database objects ?
TABLES, VIEWS, INDEXES, SYNONYMS, SEQUENCES, TABLESPACES etc
What is difference between Rename and Alias ?
Rename is a permanent name given to a table or column whereas Alias is a temporary
name given to a table or column which do not exist once the SQL statement is executed.
What is a view ?
A view is stored procedure based on one or more tables, it’s a virtual table.
What are various privileges that a user can grant to another user ?
SELECT, CONNECT, RESOURCES
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.
Can a primary key contain more than one columns ?
Yes
How you will avoid duplicating records in a query ?
By using DISTINCT
What is difference between SQL and SQL*PLUS ?
SQL*PLUS is a command line tool where as SQL and PL/SQL language interface and
reporting tool. Its a command line tool that allows user to type SQL commands to be executed
directly against an Oracle database. SQL is a language used to query the relational
database(DML,DCL,DDL). SQL*PLUS commands are used to format query result, Set options,
Edit SQL commands and PL/SQL.
Which datatype is used for storing graphics and images ?
LONG RAW data type is used for storing BLOB's (binary large objects).
How will you delete duplicating rows from a base table ?
DELETE FROM table_name A WHERE rowid>(SELECT min(rowid) from table_name B where
B.table_no=A.table_no);
CREATE TABLE new_table AS SELECT DISTINCT * FROM old_table;
DROP old_table
RENAME new_table TO old_table
DELETE FROM table_name A
WHERE rowid NOT IN (SELECT MAX(ROWID) FROM table_name
GROUP BY column_name)
What is difference between SUBSTR and INSTR ?
SUBSTR returns a specified portion of a string eg SUBSTR('BCDEF',4)
INSTR provides character position in which a pattern is found in a string.
eg INSTR('ABC-DC-F','-',2) output 7 (2nd occurence of '-')
output BCDE
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
There is a '%' sign in one field of a column. What will be the query to find it ?
'\' Should be used before '%'.
When you use WHERE clause and when 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.
Which is more faster - IN or EXISTS ?
EXISTS is more faster than IN because EXISTS returns a Boolean value whereas IN
returns a value.
What is a OUTER JOIN ?
Outer Join--Its a join condition used where you can query all the rows of one of the tables
in the join condition even though they don’t satisfy the join condition.
What is a pseudo column. Give some examples ?
It is a column that is not an actual column in the table.
eg USER, UID, SYSDATE, ROWNUM, ROWID, NULL, AND LEVEL.
Suppose customer table is there 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)
What is the purpose of a cluster ?
Oracle does not allow a user to specifically locate tables, since that is a part of the function
of the RDBMS. However, for the purpose of increasing performance, oracle allows a developer
to create a CLUSTER. A CLUSTER provides a means for storing data from different tables
together for faster retrieval than if the table placement were left to the RDBMS.
What is a cursor ?
Oracle uses work area to execute SQL statements and store processing information PL/SQL
construct called a cursor lets you name a work area and access its stored information A cursor is a
mechanism used to fetch more than one row in a PL/SQL block.
Difference between an implicit & an explicit cursor ?
PL/SQL declares a cursor implicitly for all SQL data manipulation statements, including
quries that return only one row. However,queries that return more than one row you must declare
an explicit cursor or use a cursor FOR loop.
Explicit cursor is a cursor in which the cursor name is explicitly assigned to a SELECT
statement via the CURSOR...IS statement. An implicit cursor is used for all SQL statements
Declare, Open, Fetch, Close. An explicit cursors are used to process multirow SELECT statements
An implicit cursor is used to process INSERT, UPDATE, DELETE and single row SELECT.
.INTO statements.
What are cursor attributes ?
%ROWCOUNT, %NOTFOUND, %FOUND, %ISOPEN
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.
Difference between NO DATA FOUND and %NOTFOUND ?
NO DATA FOUND is an exception raised only for the SELECT....INTO statements when the
where clause of the querydoes not match any rows. When the where clause of the explicit
cursor does not match any rows the %NOTFOUND attribute is set to TRUE instead.
What a SELECT FOR UPDATE cursor represent ?
SELECT......FROM......FOR......UPDATE[OF
column-reference][NOWAIT]
The
processing done in a fetch loop modifies the rows that have been retrieved by the cursor.
A convenient way of modifying the rows is done by a method with two parts: the FOR
UPDATE clause in the cursor declaration, WHERE CURRENT OF CLAUSE in an UPDATE or
declaration statement.
What 'WHERE CURRENT OF ' clause does in a cursor ?
LOOP SELECT num_credits INTO v_numcredits FROM classes WHERE dept=123 and
course=101;
UPDATE students SET current_credits=current_credits+v_numcredits WHERE CURRENT OF
X;
END LOOP
COMMIT;
END;
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.
What should be the return type for a cursor variable. Can we use a scalar data type as
return type ?
The return type for a cursor must be a record type.It can be declared explicitly as a user-defined or
%ROWTYPE can be used. eg TYPE t_studentsref IS REF
CURSOR RETURN students%ROWTYPE
How you open and close a cursor variable.Why it is required ?
OPEN cursor variable FOR SELECT...Statement
CLOSE cursor variable In order to associate a cursor variable with a particular
SELECT statement OPEN syntax is used.In order to free the resources used
for the query CLOSE
statement is used.
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.
Can cursor variables be stored in PL/SQL tables.If yes how.If not why?
No, a cursor variable points a row which cannot be stored in a two-dimensional PL/SQL table.
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.
What are different modes of parameters used in functions and procedures ?
IN,
OUT,
INOUT.
What is difference between a formal and an actual parameter ?
The variables declared in the procedure and which are passed, as arguments are called actual,
the parameters in the procedure declaration. Actual parameters contain the values that are passed
to a procedure and receive results. Formal parameters are the placeholders for the values of actual
parameters.
Can the default values be assigned to actual parameters ?
Yes
Can a function take OUT parameters. If not why ?
No. A function has to return a value, an OUT parameter cannot return a value.
What is syntax for dropping a procedure and a function ?
Drop Procedure procedure_name
Drop Function function_name
What are ORACLE PRECOMPILERS ?
Using ORACLE PRECOMPILERS ,SQL statements and PL/SQL blocks can be contained inside
3GL programs written in C,C++,COBOL,PASCAL, FORTRAN,PL/1 AND ADA.
The Precompilers are known as Pro*C,Pro*Cobol,...
This form of PL/SQL is known as embedded pl/sql,the language in which pl/sql is embedded is
known as the host language.
The prcompiler translates the embedded SQL and pl/sql ststements into calls to the precompiler
runtime library.The output must be compiled and linked with this library to creater an executable.
What is OCI. What are its uses ?
Oracle Call Interface is a method of accesing database from a 3GL program. Uses--No
precompiler is required,PL/SQL blocks are executed like other DML statements.
The OCI library provides
-functions to parse SQL statemets
-bind input variables
-bind output variables
-execute statements
-fetch the results
Difference between database triggers and form triggers ?
a) 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
b) Can be row level or statement level No distinction between row level and statement level.
c) Can manipulate data stored in Oracle tables via SQL Can manipulate data in Oracle tables as
well as variables in forms.
d) Can be fired from any session executing the triggering DML statements. Can be fired only
from the form that define the trigger.
e) Can cause other database triggers to fire.Can cause other database triggers to fire,but not other
form triggers.
What is an UTL_FILE.What are different procedures and functions associated
with it ?
UTL_FILE is a package that adds the ability to read and write to operating system files
Procedures associated with it are FCLOSE, FCLOSE_ALL and 5 procedures to output data to a
file
PUT,
PUT_LINE,
NEW_LINE,
PUTF,
FFLUSH.PUT,
FFLUSH.PUT_LINE,FFLUSH.NEW_LINE. Functions associated with it are FOPEN, ISOPEN.
Can you use a commit statement within a database trigger ?
No
What is maximum buffer size that can be specified using the DBMS_OUTPUT.ENABLE
function?
1,000,000
What is index ?
INDEX is a general term for an ORACLE / SQL feature used primarily to speed execution an
impose UNIQUENESS upon certain data. INDEX provides a faster access method to one table’s
data than doing a full table scan.
There are several types of Indexes :
UNIQUE INDEX, COMPRESSED INDEX, CONCATENATED INDEX. An Index has an entry
for each value found in the table’s Indexed field(s) ( except those with a NULL value ) and
pointer(s) to the rows having that value.
What is Data Dictionary ?
The DATA DICTIONARY is a comprehensive set of tables and views owned by the DBA
users SYS and SYSTEM, which activates when ORACLE is initially installed, and is a cental
source of information for the ORACLE RDBMS itself and for all users of ORACLE. The tables
are automatically maintained by ORACLE, and holds a set of views and tables containing
information about the database objects, users, privileges, events, and use.
What is a package ?
A PACKAGE is a PL/SQL object that groups PL/SQL types, variables, SQL cursors,
exceptions,procedures, and functions.Each package has a specification and a body. The
specification shows the object you can access when you use the package. The body fully defines
all the objects and can contain additional objects used only for the internal workings. You can
change the body (for example, by adding procedures to the packages) without invalidating any
object that uses the package.
What is Schema ?
A SCHEMA is a collection of objects.
SCHEMA objects are logical structures that directly refer to the database’s data.
SCHEMA objects include structures such as tables, views, synonyms, sequences, indexes,
clusters, stored procedures and data links.
1. What is a View ? Why is it required to define a View ?
A View is a database object that is a logical representation of a table. It is derived from a
table but has no storage space of its own and often may be used in the same manner as a table.
1. Security
2. Complex query can be replaced.
Advantage:
2. Can we create a View without a table ?
Yes, Using the FORCE option in the CREATE VIEW syntax.
Ex: CREATE FORCE VIEW view_name as SELECT column name, columnname..
FROM table_name;
3. What is the difference between a SYNONYM and a VIEW ?
A SYNONYM is a name assigned to a table or view that may thereafter be used to refer it.
If you access to another user’s table, you may create a synonym for it and refer to it by the
synonym alone, without entering the user’s name as a qualifier.
Difference: A View can be based on MULTIPLE Tables whereas a SYNONYM is based on a
single object only.
4. What is SNAPSHOT ? What is a SNAPSHOT LOG ?
A SNAPSHOT is a means of creating a local copy of remote data. A snapshot can be
used to replicate all or part of a single table, or to replicate the result of a query against multiple
tables. The refreshes of the replicated data can be done automatically by the database ( at time
intervals you specify ) or manually.Snapshot Log is the table associated with the Master Table of
the Snap shot.
5. What is a DATABASE trigger ? What is a DATABASE Procedure ?
A DATABASE TRIGGER is a stored procedure associated with a table that ORACLE7
automatically executes on one or more specified events (BEFORE or AFTER an
INSERT,UPDATE or DELETE) affecting the table. Triggers can execute for the table as a whole
or for each affected row in the table.
A PACKAGED PROCEDURE is a built-in PL/SQL procedure that is available in all
forms. Each packaged procedure executes a SQL*FORMS function, such as moving to a field or
executing a query.
8. What is a CURSOR ?
A work area in memory where ORACLE stores the current SQL statement. For a query ,
the area in memory also includes column headings and one row retrieved by the SELECT
statement.
10. Can we pass a PARAMETER to CURSOR ? What is SQL%ROWCOUNT ?
We can pass parameter to CURSOR. Eg: OPEN CUSOR(‘VASAN’).
SQL%ROWCOUNT is used to count the number of rows returned by an SQL DML statement. It
will return zero if the DML statement doesn’t return any row.
15. Can we use a funtion inside an INSERT statement ?
Yes. Eg: INSERT INTO EMP(COMM ) VALUES ( SAL*0.05 ) WHERE DEPTNO = 20;
16. What is TRUNCATE table ?
TRUNCATE table is a DDL command used to remove all the rows from the specified
table or cluster instantly. Eg: TRUNCATE TABLE table_name;
17. What is ROWID ? What are its components ?
ROWID is the logical address of a row, and it is unique within the database.The ROWID
is broken into three sections: left,middle,, and right (corresponding to 00001F20,000C, AND
0001, just shown). The numbering is in hexadecimal notation.
The left section is the block in the file, the middle is the row sequence number within the
block(numbering starts with 0, not 1), and the right is the file number within the database. Note
that the file numbers are uniquewithin the whole database. The tablespace they are
in is not
relevant to the ROWID.
ROWID can be selected, or used in a where clause, but cannot be changed by an insert,
update, or delete. However it can changeif the table it is in is exported and imported.
21. Name any ORACLE defined EXCEPTION ?
CURSOR_ALREADY_OPEN, NO_DATA_FOUND, INVALID_NUMBER.
22. Can we define our OWN EXCEPTION ? How to raise it ?
In the DECLARATION part define a variable of type exception. In the excecution part call
the exception using RAISE exception_name. In the exception part handle the exception using
WHEN exception_name.
23. What is a PRAGMA ?
It is a directive to the COMPILER, rather than a piece of executable code. Eventhough it
appears in the program, it is not executable. It gives instructions to the compiler.
24. Difference between CHAR and VARCHAR2 ?
CHAR(size) - It is a fixed length character data, size characters long. It is padded with
BLANKS ON RIGHT to the full length of size. DEFAULT - 1 bytes, MAXIMUM - 255 bytes.
VARCHAR2(size) - It is a varable length char string having a maximum of size bytes.
MAXIMUM - 2000 bytes.
25. What is a CURSOR FOR LOOP ?
The CURSOR FOR LOOP lets you implicitly OPEN a cursor, FETCH each row returned
by the query associated with the cursor and CLOSE the cursor when all rows have been processed.
26. What are the possible CONSTRAINTS defined on a TABLE ?
NOT NULL, UNIQUE KEY, PRIMARY KEY, FOREIGN KEY and CHECK constraints.
27. What is APPLICATION PARTITIONING ?
PL/SQL is the language used for both client-side Oracle forms applications and server-side
database triggers and stored procedures and there is a PL/SQl engine in both Oracle forms
Runform and the Oracle7 Server.
This means that you can take advantage of application patitioning to execute application
code on either the client or the server.
Application partitioning allows you to optimize performance and resource usage by storing
and executing procedures either locally or at the server, which makes the most sense for your
particular application and configuration.
28. Difference between a STORED PROCEDURE and a STORED FUNCTION ?
Unlike procedures, FUNCTIONS returns a VALUE to the caller. This value is returned
thro’ the RETURN command/keyword within the function.
Functions don’t use the IN, OUT | IN OUT arguments, which are available for
PROCEDURES.
29. How to RUN PROCEDURES from SQL PROMPT ?
Use EXECUTE Procedure_name command.
30. How to TRAP ERRORS in procedures ?
Use SHOW_ERRORS. this will display all the errors associated with the most recently
created procedural object. This command will check the VIEW_ERRORS data dictionary for the
ERRORS associated with the most recent compilation attempt for that procedural object.
SHOW_ERRORS will display the LINE and COLUMN NO. for each error, as well as the
text of the error message.
DBMS_OUTPUT package allows you to use 3 debugging functions within your package. You
must set ‘SERVER OUTPUT ON’ before executing the procedure object you will be debugging.
PUT
- Puts multiple o/p’s on same line.
PUT_LINE - Puts each o/p on a separate line.
NEW_LINE - Used with PUT; Signals the END of current o/p line.
38. What is the DIFFERENCE between PRE-QUERY and POST-QUERY ?
PRE-QUERY fires ONLY ONCE during EXECUTE-QUERY or COUNT-QUERY
processing, just before Oracle Forms constructs and issues the SELECT statement to identify rows
that match the query criteria.
POST-QUERY fires each time for records placed on the blocks list of records.
41. What is the DIFFERENCE between EXPLICIT CURSOR & IMPLICIT CURSOR ?
IMPLICIT CURSORS are automatically opened by issuing a SELECT statement. But the
EXPLICIT cursors are to be opened using OPEN, fetching is done using FETCH and closing
using CLOSE.
42. What is the difference between ROWID and ROWNUM ?
ROWID is the logical address of the row, whereas ROWNUM returns the sequence no. in
which the row was retrieved when first feched from a table.
43. What is the RESULT of the statement ?
SELECT EMPNO, NAME,SAL FROM EMP WHERE ROWNUM >2;
Result : 0, No rows will be selected.
44. How do you evaluate performance ?
Using SQL TRACE. It is an utility that can monitor and report on database performance
when one or more queries are run against the database.
It is used to gather statistics when running the query (i.e) reports on CPU time spent on the
query, the total no. of rows processed and statistics related to parsing and cache performance.
53. What is a DEAD LOCK ?
A DEAD lock is a rare situation in which two or more user processes of a database cannot
complete their tansactions.This occurs because each process is holding a resource that the other
process requires (such as a row in a table) in order to complete.
63. What does ‘GROUP BY’ statement do ?
GROUP BY statement causes a SELECT statement to produce ONE SUMMARY ROW
for all selected rows that have identical values in one or more specified column or expressions.
Each expe\ressionin the SELECT clause must be one of the following :
1] A CONSANT
2] A Function without parameters
3] A GROUP function like SUM , AVG.
4] Matched IDENTICALLY to a expression in the ‘GROUP BY’ clause.
75. Difference between SQL and PL/SQL ?
SQL is the ANSI industry standard language, used to manipulate information in a
relational database.
PL/SQL is the procedural language extension to Oracle’s SQL language.
SQL
PL/SQL
1. It is flexible, Powerful and easy to learn. 1. PL/SQL block can contain any no. of
SQL statements combined with the
2. It is a non-procedural language. It
following
:
a] Processes set of records rather than a] Flow of control statements such as
IF..THEN, ELSE, EXIT and GOTO.
just one at a time and
b] Provides automatic navigation to the b] Repetition statements such as FOR ..
LOOP and WHILE .. LOOP.
data.
c] Assignment statements such as X := Y +
3. It provides commands for avariety of Z
tasks including :
2. PL/SQL allows you to logically group a
a] Querying data
b] Creating,Updating and Replacing set of statements and send them to the
RDBMS as a single block.
objects and Inserting, Updating
and Deleting rows.
3. Procedural capabilities.
4] All RDBMS supports SQL
Thus one can transfer the skills gained 4. Improved performance.
5. Enhanced productivity
with SQL from one
6. Portability
RDBMS to another.
Programs written in SQL are portable,
they can often be moved from one database 7. Integration with the RDBMS.
to another with little modification.
77. What is the purpose of OUTER JOIN ?
An OUTER JOIN returns all the rows returned by simple join as well as those rows from
one table that do not match any row from the other table. The symbol (+) represents the outer join.
78. Difference between EQUI JOIN and OUTER JOIN ?
EQUI JOIN returns rows from both the tables provided they both have the same
column_name in the where clause. The symbol (=) represents the EQUI JOIN.
For OUTER JOIN see previous answer.
79. Define NORMALIZATION ?
NORMALIZATION is the process of putting things right, making them normal. It is a
part of analysis necessary to understand a business, and build a useful application.
The normalization of data ensures
a] Minimization of duplication of data.
b] Providing flexibility to support different funtional requirements.
c] Enabling the model to be translated to database design.
STEPS INVOLVED IN NORMALIZATION
1] Ensure that all the ENTITIES are uniquely identified by a combination of attributes.
2] Remove repeated attributes or group of attributes, to place the entities in the first
normal form.
3] Remove attributes that are dependent on only part of the identifier.
4] Remove attributes that are dependent on attributes which are not part of the identifier.
85. What is the Purpose of ERASE command ?
ERASE removes an indicated Global variable & releases the memory associated with it
What is LookUp table ?
When a foreign key exists in a table, the foreign key's table is sometimes referred to as a
lookup table. The DEPARTMENT table in our example is a lookup table for the EMPLOYEE
table. The value of an employee's department can be looked up in the DEPARTMENT table.
MULTIPLE CHOICE QUESTIONS
11. The purpose of defining an index is
(A) Enhance Sorting Performance
(C) Achieve Normalization
(B) Enhance Searching Performance
(D) All of the above
12. A transaction does not necessarily need to be
(A) Consistent
(B) Repeatable
(C) Atomic
(D) Isolated
13. To group users based on common access permission one should use
(A) User Groups
(B) Roles
(C) Grants
(D) None of the above
14. PL/SQL uses which of the following
(A) No Binding
(B) Early Binding
(C) Late Binding
(D) Deferred Binding
15. Which of the constraint can be defined at the table level as well as at the column level
(A) Unique
(B) Not Null
(C) Check
(D) All the above
16. To change the default date format in a SQLPLUS Session you have to
(A) Set the new format in the DATE_FORMAT key in the windows Registry.
(B) Alter session to set NLS_DATE-FORMAT.
(C) Change the Config.ora File for the date base.
(D) Change the User Profile USER-DATE-FORMAT.
17. Which of the following is not necessarily an advantages of using a package rather than
independent stored procedure in data base.
(A) Better performance.
(B) Optimized memory usage.
(C) Simplified Security implementation.
(D) Encapsulation.
18. Integrity constrains are not checked at the time of
(A) DCL Statements.
(B) DML Statements.
(C) DDL Statements.
(D) It is checked all the above cases.
19. Roll Back segment is not used in case of a
(A) DCL Statements.
(B) DML Statements.
(C) DDL Statements.
(D) all of the above.
QUERIES
Where do we use distinct keyword ?
Distinct is used to avoid duplicating records…………………
DELETE
FROM table_name A
WHERE rowid>(SELECT min(rowid) from table_name B where
B.table_no=A.table_no);
CREATE TABLE new_table AS SELECT DISTINCT * FROM old_table;
DROP old_table
RENAME new_table TO old_table
DELETE FROM table_name A
WHERE rowid NOT IN (SELECT MAX(ROWID) FROM table_name
GROUP BY column_name)
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
Guidelines for developers working with Databases
•
Should follow the Hungarian Style in naming the Database name (SQL server), Schema
name(Oracle), field/column name in the respective databases.
Example:
EmployeeName ------ Correct
EmpName, empname, emp_name ------ Incorrect
•
If the Column/Table name exceeds more than 30 characters the developer can go for
abbreviated names, but it should be completely relevant to the work what the table is
doing.
For Example: The ProjectSpecificPreferencesDetails Table can be named ProjSpecPrefDetails,
which is meaningful and also satisfies the field/column’s length.
•
Avoid using UnderScores( _ ) while naming Columns and Tables.
•
Should use the concepts of Stored Procedures (SQL Server), Procedures (Oracle),
Functions, Triggers where ever necessary in the database design Try to avoid unnecessary
connections in the database server in a loop. Using Procedures,
Functions and Triggers solves this problem. Another alternative is to get the whole data
into the client and try to solve the problem in the client level only, instead of interacting
with the server for several times in a loop.
•
Should follow the Normalization concepts properly. Try to achieve the Third Normal Form
for the data base which is designed, it is considered to be more efficient.(Normal Forms are
discussed below)
•
No table in the database should be independent. Every table should be related with one or
the other table.
•
Should follow the concept of index in the database. Multiple indexing is advisable if there
is an assumption of storing huge data. Retrieval of data will be faster if indexes are used.