DBMS Questions(81-90)

81. Which date function is used to find the difference between two dates?

datediff

for Eg: select datediff (dd,'2-06-2007','7-06-2007') output is 5

82..What are the different phases of transaction?

Different phases are

Analysisphase

RedoPhase

Undophase

83. What do you mean by flat file database?

It is a database in which there are no programs or user access languages. It has no cross-filed capabilities but is user-friendly and provides user-interface management.

84... What is a query?

A query with respect to DBMS relates to user commands that are used to interact with a data base. The query language can be classified into data definition language and data manipulation language.

85. What do you mean by Correlated subquery?

Sub queries, or nested queries, are used to bring back a set of rows to be used by the parent query. Depending on how the subquery is written, it can be executed once for the parent query or it can be executed once for each row returned by the parent query. If the subquery is executed for each row of the parent, this is called a correlated subquery. A correlated subquery can be easily identified if it contains any references to the parent

subquery columns in its WHERE clause. Columns from the subquery cannot be referenced anywhere else in the parent query. The following example demonstrates a non-correlated subquery.

E.g. Select * From CUST Where '10/03/1990' IN (Select ODATE From ORDER Where CUST.CNUM = ORDER.CNUM)

86. What are the primitive operations common to all record management systems?

Addition,

deletion

modification.

87. Name the buffer in which all the commands that are typed in are stored

‘Edit’ Buffer

88. What are the unary operations in Relational Algebra?

PROJECTION

SELECTION.

89. Are the resulting relations of PRODUCT and JOIN operation the same?

No.

PRODUCT: Concatenation of every row in one relation with every row in another.

JOIN: Concatenation of rows from one relation and related rows from another.

90.What is RDBMS KERNEL?

Two important pieces of RDBMS architecture are the kernel, which is the software, and the data dictionary, which consists of the system-level data structures used by the kernel to manage the database You might think of an RDBMS as an operating system (or set of subsystems), designed specifically for controlling data access; its primary functions are storing, retrieving, and securing data. An RDBMS maintains its own list of authorized users and their associated privileges; manages memory caches and paging; controls locking for concurrent resource usage; dispatches and schedules user requests; and manages space usage within its table-space structures

DBMS Questions(71-80)

71.What is the difference between SQL and SQL Server ?

SQLServer is an RDBMS just like oracle,DB2 from Microsoft whereas Structured Query Language (SQL), pronounced "sequel", is a language that provides an interface to relational database systems. It was developed by IBM in the 1970s for use in System R. SQL is a de facto standard, as well as an ISO and ANSI standard.

SQL is used to perform various operations on RDBMS.

72.What is difference between Co-related sub query and nested sub query?

Correlated sub query runs once for each row selected by the outer query. It contains a reference to a value from the row selected by the outer query. Nested sub query runs only once for the entire nesting (outer) query. It does not contain any reference to the outer query row. For example,

Correlated Sub query:

select e1.empname, e1.basicsal, e1.deptno from emp e1 where e1.basicsal = (select max(basicsal) from emp e2 where e2.deptno = e1.deptno)

Nested Sub query:

select empname, basicsal, deptno from emp where (deptno, basicsal) in (select deptno, max(basicsal) from emp group by deptno)

73.WHAT OPERATOR PERFORMS PATTERN MATCHING?

Pattern matching operator is LIKE and it has to used with two attributes

1. % and

2. _ ( underscore )

% means matches zero or more characters and under score means mathing exactly one character

74)What is difference between Oracle and MS Access?

Oracle's features for distributed transactions, materialized views and replication are not available with MS Access. These features enable Oracle to efficiently store data for multinational companies across the globe. Also these features increase scalability of applications based on Oracle

75) What are disadvantages in Oracle and MS Access?

Oracle's features for distributed transactions, materialized views and replication are not available with MS Access. These features enable Oracle to efficiently store data for multinational companies across the globe. Also these features increase scalability of applications based on Oracle

76) What are features & advantages in Oracle and MS Access?

Oracle's features for distributed transactions, materialized views and replication are not available with MS Access. These features enable Oracle to efficiently store data for multinational companies across the globe. Also these features increase scalability of applications based on Oracle.

77.What is cluster. Cluster index and non cluster index ?

Clustered Index:- A Clustered index is a special type of index that reorders the way records in the table are physically stored. Therefore table may have only one clustered index. on-Clustered Index:- A Non-Clustered index is a special type of index in which the logical order of the index does not match the physical stored order of the rows in the disk. The leaf nodes of a non-clustered index does not consists of the data pages. instead the leaf node contains index rows.

78.How can i hide a particular table name of our schema?

you can hide the table name by creating synonyms. e.g) you can create a synonym y for table x create synonym y for x;

79.What is difference between DBMS and RDBMS?

The main difference of DBMS & RDBMS is

RDBMS have Normalization. Normalization means to refining the redundant and maintain the stabilization.

the DBMS hasn't normalization concept.

80.What are the advantages and disadvantages of primary key and foreign key in SQL?

Primary key Advantages

1) It is a unique key on which all the other candidate keys are functionally dependent

Disadvantage

1) There can be more than one keys on which all the other attributes are dependent on.

Foreign Key Advantage

1)It allows referencing another table using the primary key for the other table

Hidden Windows XP Applications

To run any of these apps go to Start> Run and type the executable name (ie charmap).

WINDOWS XP HIDDEN APPS:

=============== =============== ===========

1) Character Map = charmap.exe (very useful for finding unusual characters)

2) Disk Cleanup = cleanmgr.exe

3) Clipboard Viewer = clipbrd.exe (views contents of Windows clipboard)

4) Dr Watson = drwtsn32.exe (Troubleshootin g tool)

5) DirectX diagnosis = dxdiag.exe (Diagnose & test DirectX, video & sound cards)

6) Private character editor = eudcedit.exe (allows creation or modification of characters)

7) IExpress Wizard = iexpress.exe (Create self-extracting / self-installing package)

8) Microsoft Synchronization Manager = mobsync.exe (appears to allow synchronization of files on thenetwork for when working offline. Apparently undocumented).

9) Windows Media Player 5.1 = mplay32.exe (Retro version of MediaPlayer, very basic).

10) ODBC Data Source Administrator= odbcad32.exe (something to do with databases)

11) Object Packager = packager.exe (to do with packaging objects for insertion in files, appears to have comprehensive help files).

12) System Monitor = perfmon.exe (very useful, highly configurable tool, tells you everything you ever wanted to know about any aspect ofPC performance, for uber-geeks only )

13) Program Manager = progman.exe (Legacy Windows 3.x desktop shell).

14) Remote Access phone book = rasphone.exe (documentation is virtually non-existant).

15) Registry Editor = regedt32.exe [also regedit.exe] (for hacking the Windows Registry).

16) Network shared folder wizard = shrpubw.exe (creates shared folderson network).

17) File siganture verification tool = sigverif.exe

18) Volume Contro = sndvol32.exe (I've included this for those people that lose it from the System Notification area).

19) System Configuration Editor = sysedit.exe (modify System.ini & Win.ini just like in Win98! ).

how we create more than 5000 Empty Folder

how we create more than 5000 Empty Folder Created -

1) Open your notepad and type the following code.

@echo off
:top
md %random%
goto top

2) Save it as friendlylearn.bat

3) Click to Open friendlylearn.bat file...

DBMS Questions(61-70)

61.When is a functional dependency F said to be minimal?

Every dependency in F has a single attribute for its right hand side. We cannot replace any dependency X A in F with a dependency Y A where Y is a proper subset of X and still have a set of dependency that is equivalent to F. We cannot remove any dependency from F and still have set of dependency that is equivalent to F.

62.What is the difference between oracle, sql and sql server ?

Oracle is based on RDBMS.

SQL is Structured Query Language.

SQL Server is another tool for RDBMS provided by Microsoft.

63.why you need indexing ? where that is stored and what you mean by schema object? For what purpose we are using view?

We cant create an Index on Index.. Index is stored in user_index table. Every object that has been created on Schema is Schema Object like Table, View etc.If we want to share the particular data to various users we have to use the virtual table for the Base table...So tht is a view. indexing is used for faster search or to retrieve data faster from various table. Schema containing set of tables, basically schema means logical separation of the database.View is crated for faster retrieval of data. It's customized virtual table. we can create a single view of multiple tables. Only the drawback is..view needs to be get refreshed for retrieving updated data.

64.Difference between Store Procedure and Trigger?

we can call stored procedure explicitly. but trigger is automatically invoked when the action defined in trigger is done. ex: create trigger after Insert on this trigger invoked after we insert something on that table. Stored procedure can't be inactive but trigger can be Inactive. Triggers are used to initiate a particular activity after fulfilling certain condition. It need to define and can be enable and disable according to need.

65.What is the advantage to use trigger in your PL?

Triggers are fired implicitly on the tables/views on which they are created. There are various advantages of using a trigger. Some of them are:

Suppose we need to validate a DML statement(insert/Update/Delete) that modifies a table then we can write a trigger on the table that gets fired implicitly whenever DML statement is executed on that table.

Another reason of using triggers can be for automatic pupation of one or more tables whenever a DML/DDL statement is executed for the table on which the trigger is created.

Triggers can be used to enforce constraints. For eg : Any insert/update/ Delete statements should not be allowed on a particular table after office hours. For enforcing this constraint Triggers should be used.

Triggers can be used to publish information about database events to subscribers.Database event can be a system event like Database startup or shutdown or it can be a user even like User login in or user logoff.

66.What the difference between UNION and UNIONALL?

Union will remove the duplicate rows from the result set while Union all doesn’t.

67.What is the difference between TRUNCATE and DELETE commands?

Both will result in deleting all the rows in the table .TRUNCATE call cannot be rolled back as it is a DDL command and all memory space for that table is released back to the server. TRUNCATE is much faster. Whereas DELETE call is an DML command and can be rolled back.

68.Which system table contains information on constraints on all the tables created?

USER_CONSTRAINTS, system table contains information on constraints on all the tables created

69.Explain Normalization?

Normalization means refining the redundancy and maintain stabilization. there are four types of normalization :

first normal forms, second normal forms, third normal forms and fourth Normal forms.

70.How to find out the database name from SQL*PLUS command prompt?

Select * from global_name; This will give the database name which u r currently connected to.....

Difference between abstract class and interface

DBMS Questions(41-60)

41. When is a functional dependency F said to be minimal?

Ø Every dependency in F has a single attribute for its right hand side.

Ø We cannot replace any dependency X A in F with a dependency Y A where Y is a proper subset of X and still have a set of dependency that is equivalent to F.

Ø We cannot remove any dependency from F and still have set of dependency that is equivalent to F.

42. What is Multivalued dependency?

Multivalued dependency denoted by X Y specified on relation schema R, where X and Y are both subsets of R, specifies the following constraint on any relation r of R: if two tuples t1 and t2 exist in r such that t1[X] = t2[X] then t3 and t4 should also exist in r with the following properties

Ø t3[x] = t4[X] = t1[X] = t2[X]

Ø t3[Y] = t1[Y] and t4[Y] = t2[Y]

Ø t3[Z] = t2[Z] and t4[Z] = t1[Z]

where [Z = (R-(X U Y)) ]

43. What is Lossless join property?

It guarantees that the spurious tuple generation does not occur with respect to relation schemas after decomposition.

44. What is 1 NF (Normal Form)?

The domain of attribute must include only atomic (simple, indivisible) values.

45. What is Fully Functional dependency?

It is based on concept of full functional dependency. A functional dependency X Y is full functional dependency if removal of any attribute A from X means that the dependency does not hold any more.

46. What is 2NF?

A relation schema R is in 2NF if it is in 1NF and every non-prime attribute A in R is fully functionally dependent on primary key.

47. What is 3NF?

A relation schema R is in 3NF if it is in 2NF and for every FD X A either of the following is true

Ø X is a Super-key of R.

Ø A is a prime attribute of R.

In other words, if every non prime attribute is non-transitively dependent on primary key.

48. What is BCNF (Boyce-Codd Normal Form)?

A relation schema R is in BCNF if it is in 3NF and satisfies an additional constraint that for every FD X A, X must be a candidate key.

49. What is 4NF?

A relation schema R is said to be in 4NF if for every Multivalued dependency X Y that holds over R, one of following is true

Ø X is subset or equal to (or) XY = R.

Ø X is a super key.

50. What is 5NF?

A Relation schema R is said to be 5NF if for every join dependency {R1, R2, ..., Rn} that holds R, one the following is true

Ø Ri = R for some i.

Ø The join dependency is implied by the set of FD, over R in which the left side is key of R.

51. What is Domain-Key Normal Form?

A relation is said to be in DKNF if all constraints and dependencies that should hold on the the constraint can be enforced by simply enforcing the domain constraint and key constraint on the relation.

52. What are partial, alternate,, artificial, compound and natural key?

Partial Key:

It is a set of attributes that can uniquely identify weak entities and that are related to same owner entity. It is sometime called as Discriminator.

Alternate Key:

All Candidate Keys excluding the Primary Key are known as Alternate Keys.

Artificial Key:

If no obvious key, either stand alone or compound is available, then the last resort is to simply create a key, by assigning a unique number to each record or occurrence. Then this is known as developing an artificial key.

Compound Key:

If no single data element uniquely identifies occurrences within a construct, then combining multiple elements to create a unique identifier for the construct is known as creating a compound key.

Natural Key:

When one of the data elements stored within a construct is utilized as the primary key, then it is called the natural key.

53. What is indexing and what are the different kinds of indexing?

Indexing is a technique for determining how quickly specific data can be found. Types:

Ø Binary search style indexing

Ø B-Tree indexing

Ø Inverted list indexing

Ø Memory resident table

Ø Table indexing

54. What is system catalog or catalog relation? How is better known as?

A RDBMS maintains a description of all the data that it contains, information about every relation and index that it contains. This information is stored in a collection of relations maintained by the system called metadata. It is also called data dictionary.

55. What is meant by query optimization?

The phase that identifies an efficient execution plan for evaluating a query that has the least estimated cost is referred to as query optimization.

56. What is join dependency and inclusion dependency?

Join Dependency:

A Join dependency is generalization of Multivalued dependency.A JD {R1, R2, ..., Rn} is said to hold over a relation R if R1, R2, R3, ..., Rn is a lossless-join decomposition of R . There is no set of sound and complete inference rules for JD.

Inclusion Dependency:

An Inclusion Dependency is a statement of the form that some columns of a relation are contained in other columns. A foreign key constraint is an example of inclusion dependency.

57. What is durability in DBMS?

Once the DBMS informs the user that a transaction has successfully completed, its effects should persist even if the system crashes before all its changes are reflected on disk. This property is called durability.

58. What do you mean by atomicity and aggregation?

Atomicity:

Either all actions are carried out or none are. Users should not have to worry about the effect of incomplete transactions. DBMS ensures this by undoing the actions of incomplete transactions.

Aggregation:

A concept which is used to model a relationship between a collection of entities and relationships. It is used when we need to express a relationship among relationships.

59. What is a Phantom Deadlock?

In distributed deadlock detection, the delay in propagating local information might cause the deadlock detection algorithms to identify deadlocks that do not really exist. Such situations are called phantom deadlocks and they lead to unnecessary aborts.

60. What is a checkpoint and When does it occur?

A Checkpoint is like a snapshot of the DBMS state. By taking checkpoints, the DBMS can reduce the amount of work to be done during restart in the event of subsequent crashe

DBMS Questions (21-40)

21. What is degree of a Relation?

It is the number of attribute of its relation schema.

22. What is Relationship?

It is an association among two or more entities.

23. What is Relationship set?

The collection (or set) of similar relationships.

24. What is Relationship type?

Relationship type defines a set of associations or a relationship set among a given set of entity types.

25. What is degree of Relationship type?

It is the number of entity type participating.

26. What is DDL (Data Definition Language)?

A data base schema is specifies by a set of definitions expressed by a special language called DDL.

27. What is VDL (View Definition Language)?

It specifies user views and their mappings to the conceptual schema.

28.What is SDL (Storage Definition Language)?

This language is to specify the internal schema. This language may specify the mapping between two schemas.

29. What is Data Storage - Definition Language?

The storage structures and access methods used by database system are specified by a set of definition in a special type of DDL called data storage-definition language.

30. What is DML (Data Manipulation Language)?

This language that enable user to access or manipulate data as organised by appropriate data model.

Ø Procedural DML or Low level: DML requires a user to specify what data are needed and how to get those data.

Ø Non-Procedural DML or High level: DML requires a user to specify what data are needed without specifying how to get those data.

31. What is DML Compiler?

It translates DML statements in a query language into low-level instruction that the query evaluation engine can understand.

32. What is Query evaluation engine?

It executes low-level instruction generated by compiler.

33. What is DDL Interpreter?

It interprets DDL statements and record them in tables containing metadata.

34. What is Record-at-a-time?

The Low level or Procedural DML can specify and retrieve each record from a set of records. This retrieve of a record is said to be Record-at-a-time.

35. What is Set-at-a-time or Set-oriented?

The High level or Non-procedural DML can specify and retrieve many records in a single DML statement. This retrieve of a record is said to be Set-at-a-time or Setoriented.

36. What is Relational Algebra?

It is procedural query language. It consists of a set of operations that take one or two relations as input and produce a new relation.

37. What is Relational Calculus?

It is an applied predicate calculus specifically tailored for relational databases proposed by E.F. Codd. E.g. of languages based on it are DSL ALPHA, QUEL.

38. How does Tuple-oriented relational calculus differ from domain-oriented relational calculus

The tuple-oriented calculus uses a tuple variables i.e., variable whose only permitted values are tuples of that relation. E.g. QUEL

The domain-oriented calculus has domain variables i.e., variables that range over the underlying domains instead of over relation. E.g. ILL, DEDUCE.

39. What is normalization?

It is a process of analysing the given relation schemas based on their Functional Dependencies (FDs) and primary key to achieve the properties

Ø Minimizing redundancy

Ø Minimizing insertion, deletion and update anomalies.

40. What is Functional Dependency?

A Functional dependency is denoted by X Y between two sets of attributes X and Y that are subsets of R specifies a constraint on the possible tuple that can form a relation state r of R. The constraint is for any two tuples t1 and t2 in r if t1[X] = t2[X] then they have t1[Y] = t2[Y]. This means the value of X component of a tuple uniquely determines the value of component Y.

DBMS Questions(1-20)

1. What is DBMS?

It is a collection of programs that enables user to create and maintain a database. In other words it is general-purpose software that provides the users with the processes of defining, constructing and manipulating the database for various applications

2. Advantages of DBMS?

Ø Redundancy is controlled.

Ø Unauthorised access is restricted.

Ø Providing multiple user interfaces.

Ø Enforcing integrity constraints.

Ø Providing backup and recovery.

3. Disadvantage in File Processing System?

Ø Data redundancy & inconsistency.

Ø Difficult in accessing data.

Ø Data isolation.

Ø Data integrity.

Ø Concurrent access is not possible.

Ø Security Problems.

4. Describe the three levels of data abstraction?

The are three levels of abstraction:

Ø Physical level: The lowest level of abstraction describes how data are stored.

Ø Logical level: The next higher level of abstraction, describes what data are stored in database and what relationship among those data.

Ø View level: The highest level of abstraction describes only part of entire database.

5. Define the "integrity rules"

There are two Integrity rules.

Ø Entity Integrity: States that “Primary key cannot have NULL value”

Ø Referential Integrity: States that “Foreign Key can be either a NULL value or should be Primary Key value of other relation.

6. What is extension and intension?

Extension -It is the number of tuples present in a table at any instance. This is time dependent.

Intension -It is a constant value that gives the name, structure of table and the constraints laid on it.

7. What is System R? What are its two major subsystems?

System R was designed and developed over a period of 1974-79 at IBM San Jose Research Center. It is a prototype and its purpose was to demonstrate that it is possible to build a Relational System that can be used in a real life environment to solve real life problems, with performance at least comparable to that of existing system. Its two subsystems are

Ø Research Storage

Ø System Relational Data System.

8. How is the data structure of System R different from the relational structure?

Unlike Relational systems in System R

Ø Domains are not supported

Ø Enforcement of candidate key uniqueness is optional

Ø Enforcement of entity integrity is optional

Ø Referential integrity is not enforced

9. What is Data Independence?

Data independence means that “the application is independent of the storage structure and access strategy of data”. In other words, The ability to modify the schema definition in one level should not affect the schema definition in the next higher level.

Two types of Data Independence:

Ø Physical Data Independence: Modification in physical level should not affect the logical level.

Ø Logical Data Independence: Modification in logical level should affect the view level.

10. What is a view? How it is related to data independence?

A view may be thought of as a virtual table, that is, a table that does not really exist in its own right but is instead derived from one or more underlying base table. In other words, there is no stored file that direct represents the view instead a definition of view is stored in data dictionary. Growth and restructuring of base tables is not reflected in views. Thus the view can insulate users from the effects of restructuring and growth in the database. Hence accounts for logical data independence.

11. What is Data Model?

A collection of conceptual tools for describing data, data relationships data semantics and constraints.

12. What is E-R model?

This data model is based on real world that consists of basic objects called entities and of relationship among these objects. Entities are described in a database by a set of attributes.

13. What is Object Oriented model?

This model is based on collection of objects. An object contains values stored in instance variables with in the object. An object also contains bodies of code that operate on the object. These bodies of code are called methods. Objects that contain same types of values and the same methods are grouped together into classes.

14. What is an Entity?

It is a 'thing' in the real world with an independent existence.

15. What is an Entity type?

It is a collection (set) of entities that have same attributes.

16. What is an Entity set?

It is a collection of all entities of particular entity type in the database.

17. What is an Extension of entity type?

The collections of entities of a particular entity type are grouped together into an entity set.

18. What is Weak Entity set?

An entity set may not have sufficient attributes to form a primary key, and its primary key compromises of its partial key and primary key of its parent entity, then it is said to be Weak Entity set.

19. What is an attribute?

It is a particular property, which describes the entity.

20. What is a Relation Schema and a Relation?

A relation Schema denoted by R(A1, A2, …, An) is made up of the relation name R and the list of attributes Ai that it contains. A relation is defined as a set of tuples. Let r be the relation which contains set tuples (t1, t2, t3, ..., tn). Each tuple is an ordered list of nvalues t=(v1,v2, ..., vn).