What is Interface in C#? What are the benefits of using Interface?

 

Interface: An interface contains definitions for a group of related functionalities that a non-abstract class or a struct must implement.

Interfaces can contain instance methods, properties, events, indexers, or any combination of those four member types. Interfaces may contain static constructors, fields, constants, or operators.

Benefits: Interface helps us to implement all of Object Oriented Programming concepts. There are several benefits of using interfaces in .NET, including:

1. Loose Coupling:  Interface allows us developing very loosely coupled system. An interface defines a contract that a class must follow. By using an interface, you can ensure that the class implementing it adheres to a specific set of rules and functionality.

2. Abstraction: Interface helps us developing secured system by implementing abstraction. It is a contract that contains properties and method signatures and implementation is done in inherited class. Thus it helps hiding implementation of internal business logic from external systems.

3. Inheritance: Interface in C# helps to achieve multiple inheritance. C# does not allow multiple class inheritance, but a class can implement multiple interfaces. This allows you to create objects with functionality from multiple sources, without the complications that can arise from multiple inheritance.

4. Polymorphism: Interfaces allow us to define polymorphism in a declarative way, unrelated to implementation. Two elements are polymorphic with respect to a set of behaviors if they realize the same interfaces.

5. Plug and Play: Interfaces are the key to the "plug-and-play" ability of an architecture.

6. Testing: Interfaces enable mocking objects which makes easier and better unit testing.

7. Dependency Injection: Interfaces are great for implementing Inversion of Control or Dependency Injection.

8. Extensibility: We can satisfy extensibility using the interfaces in C#.

9. Parallel Programming: Interfaces enable parallel application development.

10. Code Re usability: An interface can be implemented in multiple classes that enables greater code reuse. This can reduce the amount of code you need to write, and make it easier to modify or update existing code.

In conclusion we can say that using interfaces can help to create more modular, maintainable, and reusable code, while also enabling polymorphism and simplifying testing.

 

* Beginning with C# 8.0, an interface may define a default implementation for members.

How to split a comma separated string into multiple records using T-SQL function?

 Let's say you have a comma separated string like: 

split,a,comma,separated,string

 

Now you need to convert the string to follow rows:

split

a

comma

separated

string

 

Solution:

You can create a user defined UDF like the one shown below. Then, just pass in the comma separated list from another query and it will return a table with each value in a separate row. The function used here is a table valued function.

 

CREATE FUNCTION [dbo].[fnSplitStringToTable]
(
    @input nvarchar(MAX),
    @delimiter char(1) = ','
)
RETURNS
@Result TABLE
(
    Value nvarchar(MAX)
)
AS
BEGIN
    DECLARE @chIndex int
    DECLARE @item nvarchar(MAX)

    WHILE CHARINDEX(@delimiter, @input, 0) <> 0
    BEGIN
        SET @chIndex = CHARINDEX(@delimiter, @input, 0)
        SELECT @item = SUBSTRING(@input, 1, @chIndex - 1)

        IF LEN(@item) > 0
        BEGIN
            INSERT INTO @Result(Value)
            VALUES (@item)
        END
        SELECT @input = SUBSTRING(@input, @chIndex + 1, LEN(@input))
    END
    IF LEN(@input) > 0
    BEGIN
        INSERT INTO @Result(Value)
        VALUES (@input)
    END
    RETURN
END

 

Here is how you can execute the function and produce results as expected:

 

 

What are the functions of Data Mining?

Data mining is defined as the process of discovering patterns in data. The process must be automatic or (more usually) semiautomatic. The patterns discovered must be meaningful in that they lead some advantage, usually an economic one.

Data mining have two major functions: 

1. Classification:

• Classification maps data into predefined groups or classes. 
• It is often referred to as supervised learning because the classes are determined before examining the data. 
• Classification creates a function from training data. The training data consist of pairs of input objects, and desired output. The output of the function can be a continuous value, or can predict a class label of the input object. 
• The task of the classification is to predict the value of the function for any valid input object after having seen only a small number of training examples.

 2. Clustering:

• Clustering is similar to classification except that the groups are not predefined, but rather defined by the data alone. 
• Clustering is alternatively referred to as unsupervised learning or segmentation. 
• It can be thought of as partitioning or segmenting the data into groups that might or might not be disjointed. 
• The clustering is usually accomplished by determining the similarity among the data on predefined attributes. The most similar data are grouped into clusters.

What is Machine Learning? What are different types of Machine Learning?

Machine Learning:

Machine learning provides the technical basis of data mining. It is a branch of artificial intelligence, which concerns the construction and study of systems that can learn from data.

For example, a machine learning system could be trained on email messages to learn to distinguish between spam and non-spam messages. After learning, it can then be used to classify new email messages into spam and non-spam folders.

Types of Machine Learning:

 
Supervised learning is basically a synonym of classification. The supervision in the learning comes from the labeled instances in the training data. 

Unsupervised learning is essentially a synonym of clustering. The learning process is unsupervised since the input instances are not class labeled. 

Semi-supervised learning is a class of machine learning technology that make use of both labeled and unlabelled instances when learning a model. 

Active learning is a machine learning approach that lets users play an active role in the learning process. An active learning approach can ask a user (e.g., a domain expert) to label an instance, which may be from a set of unlabelled instances.

What is Data Mining? What Kinds of Data can be Mined?

Data mining is also known as Knowledge Discovery from Data, or KDD for short, which turns a large collection of data into knowledge. Data mining is a multidisciplinary field including machine learning, artificial intelligence, pattern recognition, knowledge-based systems, high-performance computing, database technology, and data visualization. 

• Data mining is the process of analyzing data from different perspectives and summarizing it into useful information. 
• Data mining is the process of finding hidden information and patterns in a huge database. 
• Data mining is the extraction of implicit, previously unknown, and potentially useful information from data.

 

Data, Information, and Knowledge
Data: Data are any recorded facts, numbers, or text that can be processed by a computer - scientific data, medical data, demographic data, financial data, and marking data.

Information: The patterns, associations, or relationships among all this data can provide information.

Knowledge: Information can be converted into knowledge about historical patterns and future trends.

 

What Kinds of Data can be Mined?
The most basic forms of data for mining are come from: 

1. Database Data 
2. Data Warehouses 
3. Transactional Data

What is method overloading?

Method overloading is a polymorphism technique that allows us to have same method in different ways. Overloaded method can have different number of parameters, different parameter types, and different arrangement of parameters but with same name.

What is an interface? When to use interface over abstract class?

An interface contains definitions for a group of related functionalities that a class or a struct can implement.

Use interface over abstract class:

a. If the functionality you are creating will be useful across a wide range of disparate objects, use an interface.

b. If you are designing small, concise bits of functionality, use interfaces. If you are designing large functional units, use an abstract class.

SQL update from one Table to another based on a ID match

SQL update from one Table to another based on a ID match

While working with SQL database you might often require to update one table data based on values of a column value in another table. For this to be done successfully you might require a common id field or foreign key which will match values of both tables to update.

Here is the syntax to perform the task in SQL Server:

UPDATE table1

SET t1.Col = t2.Col

FROM table1 t1

INNER JOIN table2  t2 ON t1.ID = t2.ID;

 

To demonstrated this let us assume we have following two tables: 

Place
===========
PlaceId                 int,
name                     nvarchar(200),
ispublished           bit

PlaceDetails
==============
PlaceDetailId          int,
PlaceId                     int,
DetailsDesc             nvarchar(max),
SeoTitle                   nvarchar(max),
SeoDescription         nvarchar(max),
status                       bit

Case 1: Update status field of PlaceDetails from values of ispublished in Place table.

Solution:

UPDATE PlaceDetails

SET d.status = p.ispublished

FROM PlaceDetails d

          INNER JOIN Place p ON d.PlaceId = p.PlaceId;

Case 2: Update status field of PlaceDetails from values of ispublished in Place table only for the places that are published.

Solution: You require to add a where condition along with previous query for this purpose.

UPDATE PlaceDetails

SET d.status = p.ispublished

FROM PlaceDetails d

          INNER JOIN Place p ON d.PlaceId = p.PlaceId 

         WHERE p.ispublished='True';

Case 3: Update SeoTitle and SeoDescription field of PlaceDetails for a specific placetypes

Solution: This is a complex implementation of the query that allows you to update a table values based on a complex query result. For this purpose we consider some more tables. 

The following query is used to generate SEO Titile and SEO Description information for all of the places of a category:

SELECT p.PlaceId, p.name, 'Book a room in ' + p.name +', '+ c.Name+' | addressschool.com',
p.name +' is a '+ t.Name+' in '+c.Name+', '+n.Name +' that is located in '+d.formatted_address
FROM     Place AS p INNER JOIN
                  PlaceDetail AS d ON p.PlaceId = d.PlaceId INNER JOIN
                  City AS c ON p.CityId = c.Id inner join
                  PlaceType t on p.PlaceTypeId = t.Id INNER JOIN
                  Country AS n ON p.CountryId = n.Id
WHERE  (p.PlaceTypeId = 1)

 

Now we use the above query as a inline view in the update statement to update SeoTitle and SeoDescription information in PlaceDetails table:

 UPDATE
    PlaceDetail
SET
    PlaceDetail.name = SR.SeoTitle,
    PlaceDetail.url = SR.SeoDescription
FROM
    PlaceDetail pd
INNER JOIN
    (SELECT p.PlaceId, p.name, 'Book a room in ' + p.name +', '+ c.Name+' | addressschool.com' as SeoTitle,
    p.name +' is a '+ t.Name+' in '+c.Name+', '+n.Name +' that is located in '+d.formatted_address as SeoDescription
    FROM     Place AS p INNER JOIN
                      PlaceDetail AS d ON p.PlaceId = d.PlaceId INNER JOIN
                      City AS c ON p.CityId = c.Id inner join
                      PlaceType t on p.PlaceTypeId = t.Id INNER JOIN
                      Country AS n ON p.CountryId = n.Id
    WHERE  (p.PlaceTypeId = 1)) SR
ON
    pd.PlaceId = SR.PlaceId;

 

 Hope this will help you.

Any query and comments will be appreciated and answered.

 

 

What is SQL? Explain DQL, DML, DDL, DCL and TCL statements with examples.

Learn about SQL and categories of SQL commands like DQL, DML, DDL, DCL and TCL statements with specific command examples.

 

SQL: 

SQL stands for Structured Query Language. It is the language for database that helps retrieving, storing, and manipulation of data in a relational database.

All RDBMS like Oracle, SQL Server, MySQL, PostgresSQL, DB2 etc uses SQL as database language. NoSQL database don't use it.

SQL uses certain commands like Select, Create, Insert, Update, Drop, Truncate etc. to carry out the specific tasks in the database.

These SQL commands are primarily categorized into following categories:

1. DDL – Data Definition Language
2. DQL – Data Query Language
3. DML – Data Manipulation Language
4. DCL – Data Control Language
5. TCL – Transaction Control Language

Data Definition Language (DDL)

Data Definition Language or DDL commands are comprised of the SQL commands that are used to define the database schema and objects like tables, index, procedures, triggers etc. 

DDL commands are auto-committed, meaning that changes saved permanently in the database. 

Examples of DDL commands:

• CREATE, 
• DROP, 
• ALTER, 
• TRUNCATE, 
• COMMENT,
• RENAME 

Data Query Language (DQL) :

Data Query Language or DQL statements are used to retrieve data from database tables. It is also in some form works for inserting data.

Example of DQL commands:

• SELECT

 

Data Manipulation Language(DML): 

DML SQL commands are used to manipulate data in the database. 

DML commands are not auto-committed, meaning that changes have to committed explicitly and it can be roolback

Examples of DML commands:

• INSERT
• UPDATE
• DELETE

 

Data Control Language(DCL): 

DCL commands deal with the rights, permissions and other controls of the database system.

Examples of DCL commands:

• GRANT
• REVOKE

Transaction Control Language(TCL): 

TCL commands are used to manage the transaction at the database level. These operations are automatically committed in the database.

Examples of TCL commands:

• COMMIT
• ROLLBACK
• SAVEPOINT
• SET TRANSACTION

What is the difference between primary key and unique key in SQL Server?

How to answer DBMS interview question about the difference between primary key and unique key

This is very commonly asked interview question from SQL Server or database. Following is the answer of this question:

1. By default, Primary key creates clustered index in the table but unique key creates non-clustered index.

2. Primary key column does not accept any null values, where as a unique key column accept only one null value.

3. A table can have only one primary key. On the other hand a table can have more than one unique key.

4. Duplicate values are not allowed in primary key where as duplicate value will be accepted if one or more key parts are null

5. The purpose of implementing primary key is to enforce integrity between entities of database, on the other hand the purpose of unique key is to enforce unique data within the table.