Can you explain Fourth Normal Form and Fifth Normal Form

In fourth normal form it should not contain two or more independent multi-v about an entity and it should satisfy “Third Normal form”.

Fifth normal form deals with reconstructing information from smaller pieces of information. These smaller pieces of information can be maintained with less redundancy.

What is order by clause

ORDER BY clause helps to sort the data in either ascending order to descending order.
Ascending order sort query:

SELECT name,age FROM pcdsEmployee ORDER BY age ASC

Descending order sort query

SELECT name FROM pcdsEmployee ORDER BY age DESC

What is SQLinjection

It is a Form of attack on a database-driven Web site in which the attacker executes unauthorized SQL commands by taking advantage of insecure code on a system connected to the Internet, bypassing the firewall. SQL injection attacks are used to steal information from a database from which the data would normally not be available and/or to gain access to an organization’s host computers through the computer that is hosting the database.

SQL injection attacks typically are easy to avoid by ensuring that a system has strong input validation.

As name suggest we inject SQL which can be relatively dangerous for the database. Example this is a simple SQL

SELECT email, passwd, login_id, full_name

FROM members WHERE email = ‘x’

Now somebody does not put “x” as the input but puts “x ; DROP TABLE members;”.

So the actual SQL which will execute is :-

SELECT email, passwd, login_id, full_name FROM members WHERE email = ‘x’ ; DROP TABLE members;

Think what will happen to your database.

How to select the first record in a given set of rows

Select top 1 * from sales.salesperson

What is Data Mining

Data mining is a concept by which we can analyze the current data from different perspectives and summarize the information in more useful manner. It’s mostly used either to derive some valuable information from the existing data or to predict sales to increase customer market.

There are two basic aims of Data mining:-

Prediction: –

From the given data we can focus on how the customer or market will perform. For instance we are having a sale of 40000 $ per month in India, if the same product is to be sold with a discount how much sales can the company expect.

Summarization: –

To derive important information to analyze the current business scenario. For example a weekly sales report will give a picture to the top management how we are performing on a weekly basis?

What is “Group by” clause

Group by” clause group similar data so that aggregate values can be derived.

How will you find out the superior for an employee whose emp_id is 3

You can use a self-join to find the manager of an employee whose emp_id is 3

Select e.emp_id,e.emp_name, title

Fromemployee e, employee s

where e.superior_emp_id = s.employee_idand e.emp_id = 3

This should return: 1, Peter, CIO

What is the SQL “in” clause

SQL IN operator is used to see if the value exists in a group of values. For instance the below SQL checks if the Name is either ‘rohit’ or ‘Anuradha’ SELECT * FROM pcdsEmployee WHERE name IN (‘Rohit’,’Anuradha’) Also you can specify a not clause with the same. SELECT * FROM pcdsEmployee WHERE age NOT IN (17,16).

What are CODD rules

In 1969 Dr. E. F. Codd laid down some 12 rules which a DBMS should adhere in order to get the logo of a true RDBMS.

Rule 1: Information Rule.

“All information in a relational data base is represented explicitly at the logical level and in exactly one way – by values in tables.”

Rule 2: Guaranteed access Rule.

“Each and every datum (atomic value) in a relational data base is guaranteed to be logically accessible by resorting to a combination of table name, primary key value and column name.”

In flat files we have to parse and know exact location of field values. But if a DBMS is truly RDBMS you can access the value by specifying the table name, field name, for instance Customers.Fields [‘Customer Name’].

Rule 3: Systematic treatment of null values.

“Null values (distinct from the empty character string or a string of blank characters and distinct from zero or any other number) are supported in fully relational DBMS for representing missing information and inapplicable information in a systematic way, independent of data type.”.

Rule 4: Dynamic on-line catalog based on the relational model.

“The data base description is represented at the logical level in the same way as ordinary data, so that authorized users can apply the same relational language to its interrogation as they apply to the regular data.”The Data Dictionary is held within the RDBMS, thus there is no-need for off-line volumes to tell you the structure of the database.

Rule 5: Comprehensive data sub-language Rule.

“A relational system may support several languages and various modes of terminal use (for example, the fill-in-the-blanks mode). However, there must be at least one language whose statements are expressible, per some well-defined syntax, as character strings and that is comprehensive in supporting all the following items

Data Definition
View Definition
Data Manipulation (Interactive and by program).
Integrity Constraints
Transaction boundaries ( Begin , commit and rollback)

Rule 6: .View updating Rule

“All views that are theoretically updatable are also updatable by the system.”

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.”

Rule 8: Physical data independence.

“Application programs and terminal activities remain logically unimpaired whenever any changes are made in either storage representations or access methods.”

Rule 9: Logical data independence.

“Application programs and terminal activities remain logically unimpaired when information-preserving changes of any kind that theoretically permit un-impairment are made to the base tables.”

Rule 10: Integrity independence.

“Integrity constraints specific to a particular relational data base must be definable in the relational data sub-language and storable in the catalog, not in the application programs.”

Rule 11: Distribution independence.

“A relational DBMS has distribution independence.”

Rule 12: Non-subversion Rule.

“If a relational system has a low-level (single-record-at-a-time) language, that low level cannot be used to subvert or bypass the integrity Rules and constraints expressed in the higher level relational language (multiple-records-at-a-time).”

Have you heard about sixth normal form

If we want relational system in conjunction with time we use sixth normal form. At this moment SQL Server does not supports it directly.