Saturday, July 26, 2014

Interview Questions on SQL are based on following two tables, Employee Table and Employee Incentive Table.
Table Name : Employee
EMPLOYEE_IDFIRST_NAMELAST_NAMESALARYJOINING_DATEDEPARTMENT
1JohnAbraham100000001-JAN-13 12.00.00 AMBanking
2MichaelClarke80000001-JAN-13 12.00.00 AMInsurance
3RoyThomas70000001-FEB-13 12.00.00 AMBanking
4TomJose60000001-FEB-13 12.00.00 AMInsurance
5JerryPinto65000001-FEB-13 12.00.00 AMInsurance
6PhilipMathew75000001-JAN-13 12.00.00 AMServices
7TestName112365000001-JAN-13 12.00.00 AMServices
8TestName2Lname%60000001-FEB-13 12.00.00 AMInsurance

Table Name : Incentives

EMPLOYEE_REF_IDINCENTIVE_DATEINCENTIVE_AMOUNT
101-FEB-135000
201-FEB-133000
301-FEB-134000
101-JAN-134500
201-JAN-133500

SQL QUERIES INTERVIEW QUESTIONS AND ANSWERS ON "SQL SELECT" - EXAMPLES

1. Get all employee details from the employee table
 Select * from employee
2. Get First_Name,Last_Name from employee table
 Select first_name, Last_Name from employee
3. Get First_Name from employee table using alias name “Employee Name”
 Select first_name Employee Name from employee
4. Get First_Name from employee table in upper case
 Select upper(FIRST_NAME) from EMPLOYEE
5. Get First_Name from employee table in lower case
Select lower(FIRST_NAME) from EMPLOYEE
6. Get unique DEPARTMENT from employee table
select distinct DEPARTMENT from EMPLOYEE
7. Select first 3 characters of FIRST_NAME from EMPLOYEE
Oracle Equivalent of SQL Server SUBSTRING is SUBSTR, Query : select substr(FIRST_NAME,0,3) from employee

SQL Server Equivalent of Oracle SUBSTR is SUBSTRING, Query : select substring(FIRST_NAME,0,3) from employee

MySQL Server Equivalent of Oracle SUBSTR is SUBSTRING. In MySQL start position is 1, Query : select substring(FIRST_NAME,1,3) from employee
8. Get position of 'o' in name 'John' from employee table
Oracle Equivalent of SQL Server CHARINDEX is INSTR, Query : Select instr(FIRST_NAME,'o') from employee where first_name = 'John'

SQL Server Equivalent of Oracle INSTR is CHARINDEX, Query: Select CHARINDEX('o',FIRST_NAME,0) from employee where first_name = 'John'

MySQL Server Equivalent of Oracle INSTR is LOCATE, Query: Select LOCATE('o',FIRST_NAME) from employee where first_name = 'John'
9. Get FIRST_NAME from employee table after removing white spaces from right side
select RTRIM(FIRST_NAME) from employee
10. Get FIRST_NAME from employee table after removing white spaces from left side
select LTRIM(FIRST_NAME) from employee
11. Get length of FIRST_NAME from employee table
Oracle,MYSQL Equivalent of SQL Server Len is Length , Query :select length(FIRST_NAME) from employee

SQL Server Equivalent of Oracle,MYSQL Length is Len, Query :select len(FIRST_NAME) from employee
12. Get First_Name from employee table after replacing 'o' with '$'
select REPLACE(FIRST_NAME,'o','$') from employee
13. Get First_Name and Last_Name as single column from employee table separated by a '_'
Oracle Equivalent of MySQL concat is '||', Query : Select FIRST_NAME|| '_' ||LAST_NAME from EMPLOYEE

SQL Server Equivalent of MySQL concat is '+', Query : Select FIRST_NAME + '_' +LAST_NAME from EMPLOYEE

MySQL Equivalent of Oracle '||' is concat, Query : Select concat(FIRST_NAME,'_',LAST_NAME) from EMPLOYEE
14. Get FIRST_NAME ,Joining year,Joining Month and Joining Date from employee table
SQL Queries in Oracle, Select FIRST_NAME, to_char(joining_date,'YYYY') JoinYear , to_char(joining_date,'Mon'), to_char(joining_date,'dd') from EMPLOYEE

SQL Queries in SQL Server, select SUBSTRING (convert(varchar,joining_date,103),7,4) , SUBSTRING (convert(varchar,joining_date,100),1,3) , SUBSTRING (convert(varchar,joining_date,100),5,2) from EMPLOYEE

SQL Queries in MySQL, select year(joining_date),month(joining_date), DAY(joining_date) from EMPLOYEE

DATABASE SQL QUERIES INTERVIEW QUESTIONS AND ANSWERS ON "SQL ORDER BY"


15. Get all employee details from the employee table order by First_Name Ascending

Select * from employee order by FIRST_NAME asc
16. Get all employee details from the employee table order by First_Name descending

Select * from employee order by FIRST_NAME desc
17. Get all employee details from the employee table order by First_Name Ascending and Salary descending
Select * from employee order by FIRST_NAME asc,SALARY desc

SQL QUERIES INTERVIEW QUESTIONS AND ANSWERS ON "SQL WHERE CONDITION" - EXAMPLES

18. Get employee details from employee table whose employee name is “John”
Select * from EMPLOYEE where FIRST_NAME = 'John'
19. Get employee details from employee table whose employee name are “John” and “Roy”
Select * from EMPLOYEE where FIRST_NAME in ('John','Roy')
20. Get employee details from employee table whose employee name are not “John” and “Roy”
Select * from EMPLOYEE where FIRST_NAME not in ('John','Roy')

SQL QUERIES INTERVIEW QUESTIONS AND ANSWERS ON "SQL WILD CARD SEARCH" - EXAMPLES

21. Get employee details from employee table whose first name starts with 'J'
Select * from EMPLOYEE where FIRST_NAME like 'J%'
22. Get employee details from employee table whose first name contains 'o'
Select * from EMPLOYEE where FIRST_NAME like '%o%'
23. Get employee details from employee table whose first name ends with 'n'
Select * from EMPLOYEE where FIRST_NAME like '%n'

SQL QUERIES INTERVIEW QUESTIONS AND ANSWERS ON "SQL PATTERN MATCHING" - EXAMPLES

24. Get employee details from employee table whose first name ends with 'n' and name contains 4 letters
Select * from EMPLOYEE where FIRST_NAME like '___n' (Underscores)
25. Get employee details from employee table whose first name starts with 'J' and name contains 4 letters
Select * from EMPLOYEE where FIRST_NAME like 'J___' (Underscores)
26. Get employee details from employee table whose Salary greater than 600000
Select * from EMPLOYEE where Salary > 600000
27. Get employee details from employee table whose Salary less than 800000
Select * from EMPLOYEE where Salary < 800000
28. Get employee details from employee table whose Salary between 500000 and 800000
Select * from EMPLOYEE where Salary between 500000 and 800000
29. Get employee details from employee table whose name is 'John' and 'Michael'
Select * from EMPLOYEE where FIRST_NAME in ('John','Michael')

SQL QUERIES INTERVIEW QUESTIONS AND ANSWERS ON "SQL DATE FUNCTIONS" - EXAMPLES


30. Get employee details from employee table whose joining year is “2013”
 
SQL Queries in Oracle, Select * from EMPLOYEE where to_char(joining_date,'YYYY') = '2013'

SQL Queries in SQL Server, Select * from EMPLOYEE where SUBSTRING(convert(varchar,joining_date,103),7,4) = '2013'

SQL Queries in MySQL, Select * from EMPLOYEE where year(joining_date) = '2013'
31. Get employee details from employee table whose joining month is “January”
SQL Queries in Oracle, Select * from EMPLOYEE where to_char(joining_date,'MM') = '01' or Select * from EMPLOYEE where to_char(joining_date,'Mon') = 'Jan'

SQL Queries in SQL Server, Select * from EMPLOYEE where SUBSTRING(convert(varchar,joining_date,100),1,3) = 'Jan'

SQL Queries in MySQL, Select * from EMPLOYEE where month(joining_date) = '01'
32. Get employee details from employee table who joined before January 1st 2013
SQL Queries in Oracle, Select * from EMPLOYEE where JOINING_DATE < to_date('01/01/2013','dd/mm/yyyy')

SQL Queries in SQL Server (Format - “MM/DD/YYYY”), Select * from EMPLOYEE where joining_date < '01/01/2013'

SQL Queries in MySQL (Format - “YYYY-DD-MM”), Select * from EMPLOYEE where joining_date < '2013-01-01'
33. Get employee details from employee table who joined after January 31st
SQL Queries in Oracle, Select * from EMPLOYEE where JOINING_DATE > to_date('31/01/2013','dd/mm/yyyy')

SQL Queries in SQL Server and MySQL (Format - “MM/DD/YYYY”), Select * from EMPLOYEE where joining_date >'01/31/2013'

SQL Queries in MySQL (Format - “YYYY-DD-MM”), Select * from EMPLOYEE where joining_date > '2013-01-31'
35. Get Joining Date and Time from employee table
SQL Queries in Oracle, select to_char(JOINING_DATE,'dd/mm/yyyy hh:mi:ss') from EMPLOYEE

SQL Queries in SQL Server, Select convert(varchar(19),joining_date,121) from EMPLOYEE

SQL Queries in MySQL, Select CONVERT(DATE_FORMAT(joining_date,'%Y-%m-%d-%H:%i:00'),DATETIME) from EMPLOYEE
36. Get Joining Date,Time including milliseconds from employee table
SQL Queries in Oracle, select to_char(JOINING_DATE,'dd/mm/yyyy HH:mi:ss.ff') from EMPLOYEE . Column Data Type should be “TimeStamp”

SQL Queries in SQL Server, select convert(varchar,joining_date,121) from EMPLOYEE

SQL Queries in MySQL, Select MICROSECOND(joining_date) from EMPLOYEE
37. Get difference between JOINING_DATE and INCENTIVE_DATE from employee and incentives table
Select FIRST_NAME,INCENTIVE_DATE - JOINING_DATE from employee a inner join incentives B on A.EMPLOYEE_ID = B.EMPLOYEE_REF_ID
38. Get database date
SQL Queries in Oracle, select sysdate from dual

SQL Queries in SQL Server, select getdate()

SQL Query in MySQL, select now()

SQL QUERIES INTERVIEW QUESTIONS AND ANSWERS ON "SQL ESCAPE CHARACTERS" - EXAMPLES


39. Get names of employees from employee table who has '%' in Last_Name. Tip : Escape character for special characters in a query.

SQL Queries in Oracle, Select FIRST_NAME from employee where Last_Name like '%?%%'
SQL Queries in SQL Server, Select FIRST_NAME from employee where Last_Name like '%[%]%'
SQL Queries in MySQL,Select FIRST_NAME from employee where Last_Name like '%\%%'
40. Get Last Name from employee table after replacing special character with white space
SQL Queries in Oracle, Select translate(LAST_NAME,'%',' ') from employee

SQL Queries in SQL Server and MySQL, Select REPLACE(LAST_NAME,'%',' ') from employee

SQL QUERIES INTERVIEW QUESTIONS AND ANSWERS ON "SQL GROUP BY FUNCTIONS" - EXAMPLES

41. Get department,total salary with respect to a department from employee table.
Select DEPARTMENT,sum(SALARY) Total_Salary from employee group by department
42. Get department,total salary with respect to a department from employee table order by total salary descending
Select DEPARTMENT,sum(SALARY) Total_Salary from employee group by DEPARTMENT order by Total_Salary descending

SQL QUERIES INTERVIEW QUESTIONS AND ANSWERS ON "SQL MATHEMATICAL OPERATIONS USING GROUP BY" - EXAMPLES

43. Get department,no of employees in a department,total salary with respect to a department from employee table order by total salary descending
Select DEPARTMENT,count(FIRST_NAME),sum(SALARY) Total_Salary from employee group by DEPARTMENT order by Total_Salary descending
44. Get department wise average salary from employee table order by salary ascending
select DEPARTMENT,avg(SALARY) AvgSalary from employee group by DEPARTMENT order by AvgSalary asc
45. Get department wise maximum salary from employee table order by salary ascending
select DEPARTMENT,max(SALARY) MaxSalary from employee group by DEPARTMENT order by MaxSalary asc
46. Get department wise minimum salary from employee table order by salary ascending
select DEPARTMENT,min(SALARY) MinSalary from employee group by DEPARTMENT order by MinSalary asc
47. Select no of employees joined with respect to year and month from employee table
SQL Queries in Oracle, select to_char (JOINING_DATE,'YYYY') Join_Year,to_char (JOINING_DATE,'MM') Join_Month,count(*) Total_Emp from employee group by to_char (JOINING_DATE,'YYYY'),to_char(JOINING_DATE,'MM')

SQL Queries in SQL Server, select datepart (YYYY,JOINING_DATE) Join_Year,datepart (MM,JOINING_DATE) Join_Month,count(*) Total_Emp from employee group by datepart(YYYY,JOINING_DATE), datepart(MM,JOINING_DATE)

SQL Queries in MySQL, select year (JOINING_DATE) Join_Year,month (JOINING_DATE) Join_Month,count(*) Total_Emp from employee group by year(JOINING_DATE), month(JOINING_DATE)
48. Select department,total salary with respect to a department from employee table where total salary greater than 800000 order by Total_Salary descending
Select DEPARTMENT,sum(SALARY) Total_Salary from employee group by DEPARTMENT having sum(SALARY) > 800000 order by Total_Salary desc

SQL QUERIES INTERVIEW QUESTIONS AND ANSWERS ON "SQL JOINS" - EXAMPLES


49. Select first_name, incentive amount from employee and incentives table for those employees who have incentives

Select FIRST_NAME,INCENTIVE_AMOUNT from employee a inner join incentives B on A.EMPLOYEE_ID = B.EMPLOYEE_REF_ID
50. Select first_name, incentive amount from employee and incentives table for those employees who have incentives and incentive amount greater than 3000
Select FIRST_NAME,INCENTIVE_AMOUNT from employee a inner join incentives B on A.EMPLOYEE_ID = B.EMPLOYEE_REF_ID and INCENTIVE_AMOUNT > 3000
51. Select first_name, incentive amount from employee and incentives table for all employes even if they didn't get incentives
Select FIRST_NAME,INCENTIVE_AMOUNT from employee a left join incentives B on A.EMPLOYEE_ID = B.EMPLOYEE_REF_ID
52. Select first_name, incentive amount from employee and incentives table for all employees even if they didn't get incentives and set incentive amount as 0 for those employees who didn't get incentives.
SQL Queries in Oracle, Select FIRST_NAME,nvl(INCENTIVE_AMOUNT,0) from employee a left join incentives B on A.EMPLOYEE_ID = B.EMPLOYEE_REF_ID

SQL Queries in SQL Server, Select FIRST_NAME, ISNULL(INCENTIVE_AMOUNT,0) from employee a left join incentives B on A.EMPLOYEE_ID = B.EMPLOYEE_REF_ID

SQL Queries in MySQL, Select FIRST_NAME, IFNULL(INCENTIVE_AMOUNT,0) from employee a left join incentives B on A.EMPLOYEE_ID = B.EMPLOYEE_REF_ID
53. Select first_name, incentive amount from employee and incentives table for all employees who got incentives using left join
SQL Queries in Oracle, Select FIRST_NAME,nvl(INCENTIVE_AMOUNT,0) from employee a right join incentives B on A.EMPLOYEE_ID = B.EMPLOYEE_REF_ID

SQL Queries in SQL Server, Select FIRST_NAME, isnull(INCENTIVE_AMOUNT,0) from employee a right join incentives B on A.EMPLOYEE_ID = B.EMPLOYEE_REF_ID

SQL Queries in MySQL, Select FIRST_NAME, IFNULL(INCENTIVE_AMOUNT,0) from employee a right join incentives B on A.EMPLOYEE_ID = B.EMPLOYEE_REF_ID
54. Select max incentive with respect to employee from employee and incentives table using sub query
SQL Queries in Oracle, select DEPARTMENT,(select nvl(max(INCENTIVE_AMOUNT),0) from INCENTIVES where EMPLOYEE_REF_ID = EMPLOYEE_ID) Max_incentive from EMPLOYEE

SQL Queries in SQL Server, select DEPARTMENT,(select ISNULL(max(INCENTIVE_AMOUNT),0) from INCENTIVES where EMPLOYEE_REF_ID = EMPLOYEE_ID) Max_incentive from EMPLOYEE

SQL Queries in SQL Server, select DEPARTMENT,(select IFNULL (max(INCENTIVE_AMOUNT),0) from INCENTIVES where EMPLOYEE_REF_ID = EMPLOYEE_ID) Max_incentive from EMPLOYEE

ADVANCED SQL QUERIES INTERVIEW QUESTIONS AND ANSWERS ON "TOP N SALARY" - EXAMPLES

55. Select TOP 2 salary from employee table
SQL Queries in Oracle, select * from (select * from employee order by SALARY desc) where rownum < 3

SQL Queries in SQL Server, select top 2 * from employee order by salary desc

SQL Queries in MySQL, select * from employee order by salary desc limit 2
56. Select TOP N salary from employee table
SQL Queries in Oracle, select * from (select * from employee order by SALARY desc) where rownum < N + 1

SQL Queries in SQL Server, select top N * from employee

SQL Queries in MySQL, select * from employee order by salary desc limit N
57. Select 2nd Highest salary from employee table
SQL Queries in Oracle, select min(salary) from (select * from (select * from employee order by SALARY desc) where rownum < 3)

SQL Queries in SQL Server, select min(SALARY) from (select top 2 * from employee) a

SQL Queries in MySQL, select min(SALARY) from (select * from employee order by salary desc limit 2) a
58. Select Nth Highest salary from employee table
SQL Queries in Oracle, select min(salary) from (select * from (select * from employee order by SALARY desc) where rownum < N + 1)

SQL Queries in SQL Server, select min(SALARY) from (select top N * from employee) a

SQL Queries in MySQL, select min(SALARY) from (select * from employee order by salary desc limit N) a

SQL QUERIES INTERVIEW QUESTIONS AND ANSWERS ON "SQL UNION" - EXAMPLES

59. Select First_Name,LAST_NAME from employee table as separate rows
select FIRST_NAME from EMPLOYEE union select LAST_NAME from EMPLOYEE
60. What is the difference between UNION and UNION ALL ?
Both UNION and UNION ALL is used to select information from structurally similar tables. That means corresponding columns specified in the union should have same data type. For example, in the above query, if FIRST_NAME is DOUBLE and LAST_NAME is STRING above query wont work. Since the data type of both the columns are VARCHAR, union is made possible. Difference between UNION and UNION ALL is that , UNION query return only distinct values.

"ADVANCED SQL QUERIES INTERVIEW QUESTIONS AND ANSWERS"


61. Select employee details from employee table if data exists in incentive table ?

select * from EMPLOYEE where exists (select * from INCENTIVES)
Explanation : Here exists statement helps us to do the job of If statement. Main query will get executed if the sub query returns at least one row. So we can consider the sub query as "If condition" and the main query as "code block" inside the If condition. We can use any SQL commands (Joins, Group By , having etc) in sub query. This command will be useful in queries which need to detect an event and do some activity.
62. How to fetch data that are common in two query results ?
select * from EMPLOYEE where EMPLOYEE_ID INTERSECT select * from EMPLOYEE where EMPLOYEE_ID < 4

Explanation : Here INTERSECT command is used to fetch data that are common in 2 queries. In this example, we had taken EMPLOYEE table in both the queries.We can apply INTERSECT command on different tables. The result of the above query will return employee details of "ROY" because, employee id of ROY is 3, and both query results have the information about ROY.
63. Get Employee ID's of those employees who didn't receive incentives without using sub query ?
select EMPLOYEE_ID from EMPLOYEE

MINUS

select EMPLOYEE_REF_ID from INCENTIVES

 
Explanation : To filter out certain information we use MINUS command. What MINUS Command odes is that, it returns all the results from the first query, that are not part of the second query. In our example, first three employees received the incentives. So query will return employee id's 4 to 8.
64. Select 20 % of salary from John , 10% of Salary for Roy and for other 15 % of salary from employee table
SELECT FIRST_NAME, CASE FIRST_NAME WHEN 'John' THEN SALARY * .2 WHEN 'Roy' THEN SALARY * .10 ELSE SALARY * .15 END "Deduced_Amount" FROM EMPLOYEE 


Explanation : Here we are using SQL CASE statement to achieve the desired results. After case statement, we had to specify the column on which filtering is applied. In our case it is "FIRST_NAME". And in then condition, specify the name of filter like John, Roy etc. To handle conditions outside our filter, use else block where every one other than John and Roy enters.
65. Select Banking as 'Bank Dept', Insurance as 'Insurance Dept' and Services as 'Services Dept' from employee table
SQL Queries in Oracle, SELECT distinct DECODE (DEPARTMENT, 'Banking', 'Bank Dept', 'Insurance', 'Insurance Dept', 'Services', 'Services Dept') FROM EMPLOYEE

SQL Queries in SQL Server and MySQL, SELECT case DEPARTMENT when 'Banking' then 'Bank Dept' when 'Insurance' then 'Insurance Dept' when 'Services' then 'Services Dept' end FROM EMPLOYEE

 Explanation : Here DECODE keyword is used to specify the alias name. In oracle we had specify, Column Name followed by Actual Name and Alias Name as arguments. In SQL Server and MySQL, we can use the earlier switch case statements for alias names.
66. Delete employee data from employee table who got incentives in incentive table
delete from EMPLOYEE where EMPLOYEE_ID in (select EMPLOYEE_REF_ID from INCENTIVES)

 Explanation : Trick about this question is that we can't delete data from a table based on some condition in another table by joining them. Here to delete multiple entries from EMPLOYEE table, we need to use Subquery. Entries will get deleted based on the result of Subquery.
67. Insert into employee table Last Name with " ' " (Single Quote - Special Character)
Tip - Use another single quote before special character

Insert into employee (LAST_NAME) values ('Test''')
68. Select Last Name from employee table which contain only numbers
Select * from EMPLOYEE where lower(LAST_NAME) = upper(LAST_NAME)

 Explanation : Here in order to achieve the desired result, we use ASCII property of the database. If we get results for a column using Lower and Upper commands, ASCII of both results will be same for numbers. If there is any alphabets in the column, results will differ.
69. Write a query to rank employees based on their incentives for a month
select FIRST_NAME,INCENTIVE_AMOUNT,DENSE_RANK() OVER (PARTITION BY INCENTIVE_DATE ORDER BY  INCENTIVE_AMOUNT DESC) AS Rank from EMPLOYEE a, INCENTIVES b where a.EMPLOYEE_ID = b.EMPLOYEE_REF_ID

 Explanation : Here in order to rank employees based on their rank for a month, DENSE_RANK keyword is used. Here partition by keyword helps us to sort the column with which filtering is done. Rank is provided to the column specified in the order by statement. The above query ranks employees with respect to their incentives for a given month.
70. Update incentive table where employee name is 'John'

Explanation : Here we need to join Employee and Incentive Table for updating the incentive amount. But for update statement joining query wont work. We need to use sub query to update the data in the incentive table. SQL Query is as shown below.
update INCENTIVES set INCENTIVE_AMOUNT = '9000' where EMPLOYEE_REF_ID =(select EMPLOYEE_ID from EMPLOYEE where FIRST_NAME = 'John' )

SQL QUERIES INTERVIEW QUESTIONS AND ANSWERS ON "SQL TABLE SCRIPTS" - EXAMPLES

71. Write create table syntax for employee table
Oracle -

CREATE TABLE EMPLOYEE (

EMPLOYEE_ID NUMBER,

FIRST_NAME VARCHAR2(20 BYTE),

LAST_NAME VARCHAR2(20 BYTE),

SALARY FLOAT(126),

JOINING_DATE TIMESTAMP (6) DEFAULT sysdate,

DEPARTMENT VARCHAR2(30 BYTE) )


SQL Server -

CREATE TABLE EMPLOYEE(

EMPLOYEE_ID int NOT NULL,

FIRST_NAME varchar(50) NULL,

LAST_NAME varchar(50) NULL,

SALARY decimal(18, 0) NULL,

JOINING_DATE datetime2(7) default getdate(),

DEPARTMENT varchar(50) NULL)
72. Write syntax to delete table employee
DROP table employee;
73. Write syntax to set EMPLOYEE_ID as primary key in employee table
ALTER TABLE EMPLOYEE add CONSTRAINT EMPLOYEE_PK PRIMARY KEY(EMPLOYEE_ID)
74. Write syntax to set 2 fields(EMPLOYEE_ID,FIRST_NAME) as primary key in employee table
ALTER TABLE EMPLOYEE add CONSTRAINT EMPLOYEE_PK PRIMARY KEY(EMPLOYEE_ID,FIRST_NAME)
75. Write syntax to drop primary key on employee table
Alter TABLE EMPLOYEE drop CONSTRAINT EMPLOYEE_PK;
76. Write Sql Syntax to create EMPLOYEE_REF_ID in INCENTIVES table as foreign key with respect to EMPLOYEE_ID in employee table
ALTER TABLE INCENTIVES ADD CONSTRAINT INCENTIVES_FK FOREIGN KEY (EMPLOYEE_REF_ID) REFERENCES EMPLOYEE(EMPLOYEE_ID)
77. Write SQL to drop foreign key on employee table
ALTER TABLE INCENTIVES drop CONSTRAINT INCENTIVES_FK;
78. Write SQL to create Orcale Sequence
CREATE SEQUENCE EMPLOYEE_ID_SEQ START WITH 0 NOMAXVALUE MINVALUE 0 NOCYCLE NOCACHE NOORDER;
79. Write Sql syntax to create Oracle Trigger before insert of each row in employee table
CREATE OR REPLACE TRIGGER EMPLOYEE_ROW_ID_TRIGGER

BEFORE INSERT ON EMPLOYEE FOR EACH ROW

DECLARE

seq_no number(12);

BEGIN

select EMPLOYEE_ID_SEQ.nextval into seq_no from dual ;

:new EMPLOYEE_ID := seq_no;

END;

SHOW ERRORS;
80. Oracle Procedure 81. Oracle View
An example oracle view script is given below

create view Employee_Incentive as select FIRST_NAME,max(INCENTIVE_AMOUNT) INCENTIVE_AMOUNT from EMPLOYEE a, INCENTIVES b where a.EMPLOYEE_ID = b.EMPLOYEE_REF_ID group by FIRST_NAME
82. Oracle materialized view - Daily Auto Refresh 
CREATE MATERIALIZED VIEW Employee_Incentive

REFRESH COMPLETE

START WITH SYSDATE

NEXT SYSDATE + 1 AS

select FIRST_NAME,INCENTIVE_DATE,INCENTIVE_AMOUNT from EMPLOYEE a, INCENTIVES b 

where a.EMPLOYEE_ID = b.EMPLOYEE_REF_ID
83. Oracle materialized view - Fast Refresh on Commit
Create materialized view log for fast refresh. Following materialized view script wont get executed if materialized view log doesn't exists


CREATE MATERIALIZED VIEW MAT_Employee_Incentive_Refresh

BUILD IMMEDIATE

REFRESH FAST ON COMMIT AS

select FIRST_NAME,max(INCENTIVE_AMOUNT) from EMPLOYEE a, INCENTIVES b

where a.EMPLOYEE_ID = b.EMPLOYEE_REF_ID group by FIRST_NAME
84. What is SQL Injection ?
SQL Injection is one of the the techniques uses by hackers to hack a website by injecting SQL commands in data fields.

Wednesday, July 23, 2014

What’s difference between Datagrid, Datalist and repeater

A Datagrid, Datalist and Repeater are all ASP.NET data Web controls.
They have many things in common like DataSource Property, DataBind Method
ItemDataBound and ItemCreated.
When you assign the DataSource Property of a Datagrid to a DataSet then each DataRow
present in the DataRow Collection of DataTable is assigned to a corresponding
DataGridItem and this is same for the rest of the two controls also. But The HTML code
generated for a Datagrid has an HTML TABLE <ROW> element created for the particular
DataRow and its a Table form representation with Columns and Rows.
For a Datalist its an Array of Rows and based on the Template Selected and the
RepeatColumn Property value We can specify how many DataSource records should
appear per HTML <table> row. In short in datagrid we have one record per row, but in
datalist we can have five or six rows per row.
For a Repeater Control, the Datarecords to be displayed depends upon the Templates
specified and the only HTML generated is the due to the Templates.
In addition to these, Datagrid has a in-built support for Sort, Filter and paging the Data,
which is not possible when using a DataList and for a Repeater Control we would require
to write an explicit code to do paging.

Tuesday, July 22, 2014

What are the various ways of authentication techniques in ASP.NET?

Selecting an authentication provider is as simple as making an entry in the web.config file
for the application. You can use one of these entries to select the corresponding built in
authentication provider:
√ <authentication mode=”windows”>
√ <authentication mode=”passport”>
√ <authentication mode=”forms”>
√ Custom authentication where you might install an ISAPI filter in IIS that
compares incoming requests to list of source IP addresses, and considers
requests to be authenticated if they come from an acceptable address. In that
case, you would set the authentication mode to none to prevent any of the
.net authentication providers from being triggered.
Windows authentication and IIS
If you select windows authentication for your ASP.NET application, you also have to
configure authentication within IIS. This is because IIS provides Windows authentication.
IIS gives you a choice for four different authentication methods:
Anonymous, basic digest and windows integrated
If you select anonymous authentication, IIS doesn’t perform any authentication, Any one
is allowed to access the ASP.NET application.
If you select basic authentication, users must provide a windows username and password
to connect. How ever this information is sent over the network in clear text, which makes
basic authentication very much insecure over the internet.
If you select digest authentication, users must still provide a windows user name and
password to connect. However the password is hashed before it is sent across the network.

Digest authentication requires that all users be running Internet Explorer 5 or later and
that windows accounts to stored in active directory.
If you select windows integrated authentication, passwords never cross the network.
Users must still have a username and password, but the application uses either the Kerberos
or challenge/response protocols authenticate the user. Windows-integrated authentication
requires that all users be running internet explorer 3.01 or later Kerberos is a network
authentication protocol. It is designed to provide strong authentication for client/server
applications by using secret-key cryptography. Kerberos is a solution to network security
problems. It provides the tools of authentication and strong cryptography over the network
to help to secure information in systems across entire enterprise
Passport authentication
Passport authentication lets you to use Microsoft’s passport service to authenticate users
of your application. If your users have signed up with passport, and you configure the
authentication mode of the application to the passport authentication, all authentication
duties are off-loaded to the passport servers.
Passport uses an encrypted cookie mechanism to indicate authenticated users. If users
have already signed into passport when they visit your site, they’ll be considered
authenticated by ASP.NET. Otherwise they’ll be redirected to the passport servers to log
in. When they are successfully log in, they’ll be redirected back to your site
To use passport authentication you have to download the Passport Software Development
Kit (SDK) and install it on your server. The SDK can be found at http://
msdn.microsoft.com/library/default.asp?url=/downloads/list/websrvpass.aps. It includes
full details of implementing passport authentication in your own applications.
Forms authentication
Forms authentication provides you with a way to handle authentication using your own
custom logic with in an ASP.NET application. The following applies if you choose forms
authentication.
√ When a user requests a page for the application, ASP.NET checks for the
presence of a special session cookie. If the cookie is present, ASP.NET assumes
the user is authenticated and processes the request.
√ If the cookie isn’t present, ASP.NET redirects the user to a web form you
provide
You can carry out whatever authentication, it check’s you like it checks your form. When
the user is authenticated, you indicate this to ASP.NET by setting a property, which
creates the special cookie to handle subsequent requests.

How does authorization work in ASP.NET?

ASP.NET impersonation is controlled by entries in the applications web.config file. The
default setting is “no impersonation”. You can explicitly specify that ASP.NET shouldn’t
use impersonation by including the following code in the file
<identity impersonate=”false”/>
It means that ASP.NET will not perform any authentication and runs with its own
privileges. By default ASP.NET runs as an unprivileged account named ASPNET. You
can change this by making a setting in the processModel section of the machine.config
file. When you make this setting, it automatically applies to every site on the server. To
user a high-privileged system account instead of a low-privileged set the userName attribute
of the processModel element to SYSTEM. Using this setting is a definite security risk, as
it elevates the privileges of the ASP.NET process to a point where it can do bad things to
the operating system.
When you disable impersonation, all the request will run in the context of the account
running ASP.NET: either the ASPNET account or the system account. This is true when
you are using anonymous access or authenticating users in some fashion. After the user
has been authenticated, ASP.NET uses its own identity to request access to resources.
The second possible setting is to turn on impersonation.
<identity impersonate =”true”/>
In this case, ASP.NET takes on the identity IIS passes to it. If you are allowing anonymous
access in IIS, this means ASP.NET will impersonate the IUSR_ComputerName account
that IIS itself uses. If you aren’t allowing anonymous access,ASP.NET will take on the
credentials of the authenticated user and make requests for resources as if it were that
user. Thus by turning impersonation on and using a non-anonymous method of
authentication in IIS, you can let users log on and use their identities within your ASP.NET
application.
Finally, you can specify a particular identity to use for all authenticated requests

<identity impersonate=”true” username=”DOMAIN\username” password=”password”/
>
With this setting, all the requests are made as the specified user (Assuming the password
it correct in the configuration file). So, for example you could designate a user for a single
application, and use that user’s identity every time someone authenticates to the
application. The drawback to this technique is that you must embed the user’s password
in the web.config file in plain text. Although ASP.NET won’t allow anyone to download
this file, this is still a security risk if anyone can get the file by other means.

Saturday, July 19, 2014

Difference Between Abstract Class and an Interface

INTRODUCTION :
In this article I am going to explain the difference between an Abstract Class and an Interface with some examples.
DIFFERENCE BETWEEN AN ABSTRACT CLASS AND AN INTERFACE:
  1. An Abstract class doesn't provide full abstraction but an interface does provide full abstraction; i.e. both a declaration and a definition is given in an abstract class but not so in an interface.
  2. Using Abstract we can not achieve multiple inheritance but using an Interface we can achieve multiple inheritance.
  3. We can not declare a member field in an Interface.
  4. We can not use any access modifier i.e. public , private , protected , internal etc. because within an interface by default everything is public.
  5. An Interface member cannot be defined using the keyword static, virtual, abstract or sealed.
A) Abstract Class : We can not create an object of an abstract class and can call the method of abstract class with the help of class name only.
Take a look at an Abstract class example:
FIG3.jpg
The Code window looks like this:
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

 namespace ConsoleApplication4
{
   abstract class M1
   {
        public int add(int a, int b)
        {
            return (a + b);
        }
    }
    class M2 :M1   
    {
        public int mul(int a, int b)
        {
            return a * b;
        }
    }
    class test   
    {
        static void Main(string[] args)
        {
            M2 ob = new M2();
            int result = ob.add(10, 20);
            Console.WriteLine("the result is {0}", result);
            Console.ReadLine();
        }
    }
}When we run it the output looks like this:

fig1.jpg

 B) An Interface : The syntax of an Interface looks like this:
interface
{
     //Interface member
}
NOTE :
  1. An Interface member can not contain code bodies.
  2. Type definition members are forbidden.
  3. Properties are defined in an interface with the help of an access block get and set, which are permitted for the property.
          e.g.   Interface myInterface
                           {
                              int myint 
                                {
                                     get;
                                     set;
                                  }
                             }
Take a look in an interface example:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

 namespace ConsoleApplication3
{
    interface MyInterface
    {
      void myMethod();
    }
    class MyClass : MyInterface
    {
      public static void Main()
      {
            MyClass cls = new MyClass();
            cls.myMethod();
      }
       public void myMethod()
      {
            Console.WriteLine("welcome to MCN IT SOLUTION");
            Console.ReadLine();
       }
    }
}After running this program we obtain output as follows:
fig2.jpg

 NOTE :  In C# , an Interface provides only those public services declared in the interface, whereas an abstract class provides the public services defined in an abstract class and those members that are inherited from the abstract class's base class.

Importent ASP.NET question and answers

What are page directives?
The first line of an ASP.NET page is the page directive; you will find it on all ASP.NET pages. These directives are instructions for the page. It begins with the @Page directive and continues with the various attributes available to this directive.
 
It’s unreasonable to expect a candidate to know all of these attributes, but a few popular ones include the following.
 
AutoEventWireup: Indicates whether page events are autowired.
CodeBehind: The name of the compiled class associated with the page.
Debug: Indicates whether the page is compiled in debug mode (includes debug symbols).
EnableTheming: Indicates whether themes are used on the page.
EnableViewState: Indicates whether view state is maintained across pages.
ErrorPage: Specifies a target URL to be used when unhandled exceptions occur.
Language: Indicates the language used when compiling inline code on the page.
Trace: Signals whether tracing is enabled on the page.

What is a master page?
 
A master page is a template for one or more Web Forms. The master page defines how the page will be laid out when presented to the user, with placeholders for content. The MasterPageFile Page Directive in a content page’s header is one way to assign a master page. The content pages rely solely on content and leave layout to the master page. ASP.NET merges the content with the master page layout when the content page is requested by a user.

What is the code behind feature of ASP.NET?
 
The code behind feature divides ASP.NET page files into two files where one defines the user interface (.aspx), while the other contains all of the logic or code (.aspx.cs for C# and .aspx.vb for VB.NET). These two files are glued together with page directives like the following line, which ties the page to the specific code behind class.
 
<![CDATA[<%@ Page language="c#" Codebehind="UICode.cs" Inherits="Library.UICode" %>
What are ASHX files?
 
ASP.NET Web handler files have an .ashx file extension. Web handlers work just like .aspx files except you don’t have to deal with the browser interface, thus no worrying about presentation. Web handlers are generally used to generate content dynamically like returning XML or an image. Web handlers use the IHttpHandler interface with the ProcessRequest() method invoked when the handler is requested. Web handlers are simpler than pages (fewer events and wiring), so they are ideal for performance-critical applications.
 
How does PostBack work?
 
PostBack is basically the ASP.NET submitting a form to it — it posts back to the current URL. The JavaScript __doPostBack function is placed on the page (look at the source within the browser) to facilitate. PostBack uses ViewState to remember controls and data. The IsPostBack property of the ASP.NET page allows you to determine if the loading of the page is the result of a postback event; this is done in the Page_Load event.
 
How can you pass values between ASP.NET pages?
 
There are numerous ways to accomplish this task; the option you choose depends on the environment. The oldest way to approach it is via the QueryString (i.e., passing values via URL); this is also one of the least secure ways because users can easily see the data and could possibly hack the site/page by changing parameter values. Next, you can use HTTP POST to pass values; these are available via a collection within the ASP.NET page. More specific to ASP.NET is the use of Session state, which makes information available to all pages within the ASP.NET application. Another approach is using public properties on the source page and accessing these properties on the target page. Also, you can use the PreviousPage property of the current page to access control information on the referring page. The last two require the source, and target pages are within the same ASP.NET application.
 
What are ASP.NET Server controls?
 
ASP.NET includes a number of built-in server controls that are the foundation of its Web programming model. They have various properties to control their behavior and appearance. These controls provide an event model where events are handled on the server (whereas HTML controls are handled in the client). Server controls have the ability to maintain state (via ViewState) across requests, and they can automatically detect the browser. With these controls, you will see the RunAt attribute (RunAt=”Server”) that signals its processing will be done on the server. A good example of these controls is the basic TextBox control (<asp:textbox runat="”Server”" xmlns:asp="#unknown">.
 
What is View State?
 
Basically, View State is how ASP.NET Web pages persists data across requests. It handles data that must be preserved between postbacks, and you can use it to store page-specific data. By default, View State is enabled on a page and its controls. This can be a problem as the amount of data and controls on a page increases resulting in more data for ASP.NET to maintain. This is accomplished via the hidden __VIEWSTATE field on a form (look at the page source in a browser), so more data in this field means a slower load time and slower overall processing, as it has to be posted to the server each time. You can limit the size of the data in View State by disabling controls that do not need to be persisted via the EnableViewState property. View State can be encrypted to address security concerns.
 
What is the global.asax file?
 

The global.asax file is an optional piece of an ASP.NET application. It is located in the root of the application directory structure. It cannot be directly loaded or requested by users. It provides a place to define application- and session-wide events. You can define your own events, but it does contain default Application events like when the application starts Application_Start and ends with Application_End. The same is true for Session events (Session_Start and Session_End).
 
How can you loop through all controls on an ASP.NET Web form?
 
You can easily traverse all controls on a form via the Web Form’s Controls collection. The GetType method can be used on each control to determine its type and how to work with it. Now, it gets tricky because the form contains a tree of controls; that is, some controls are contained within others (think of a Table). You would have to recursively loop through the controls to make sure everything is processed.
 
What is a web.config file? Machine.config?
 
The web.config is the basic configuration file for ASP.NET applications. It utilizes an XML format. It is used to define application settings, connection strings, and much more. These files can appear in multiple directories, and they are applied in a top-down approach; that is, configuration files apply to their container directory as well as all directories below it, but the configuration files in lower directories can override those in parent directories. This provides a way to granularly apply settings. The machine.config file contains ASP.NET settings for all of the applications on the server — it is at the top of the configuration file hierarchy, thus web.configs can override it.