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SQL Server 2016 Hosting - HostForLIFE.eu :: Encrypt And Decrypt Column Data In SQL Server

clock March 13, 2019 09:26 by author Peter

Recently, I worked on a project to hide sensitive data. Basically, the client wanted sensitive data to be encrypted, then accessed and decrypted by the application only. In case a hacker or an employee or a DBA accesses data directly, they can't read the field. Some perfect examples are customer's credit card number, date of birth, social security, or even medical records.

SQL Server provides a feature that allows DBAs and data developers to encrypt and save encrypted data on a column level. Once a column is encrypted, it's not readable by humans.

In this blog, let's see how this can be acheieved.
In the below example, I have used the Credit Card Number column to be encrypted.

You need to write a stored procedure to execute a set of statements and queries. Though it is not a foolproof way to encrypt or decrypt at the database level, while working on this task, I learned some good techniques and features of SQL Server.

There are 3 major factors to encrypt data at the column level, as below.

  • Master Key -  a key which is used to protect the keys of certificates and symmetric keys in the database
  • Certificates - used to encrypt the data in the database
  • Symmetric Key - can be encrypted by using many options, like certificate, password, symmetric key. There are different algorithms available for encrypting a key. The supported algorithms are DES, TRIPLE_DES, RC2, RC4, RC4_128, DESX, AES_128, AES_192, and AES_256.

So, let's start step by step and achieve the encryption and decryption.

Step 1
Create a Master Key first with the help of the below script.
use TestingDB; //This is the Test Database created.  
Create master key encryption by password ='abc123' 


Step 2
Once the Master Key is created, now it's time to create a Certificate.
Create certificate C1 with subject = 'Credit Card Data'

Step 3
Now with the help of certificate and master key create SYMMETRIC KEY.
Create symmetric key SK1 with algorithm = AES_256 encryption by certificate C1.
Once all these KEYs are created in the database, we can use those for encrypting and decrypting data.

Below is the script to encrypt the data in the column. Here I have created one TABLE named TestEncryption having 3 columns with its datatype as below. Note that the column in which we want to insert or update encrypted data should have VARBINARY as the datatype.

Id - INT
EncryptedCCNumber - varbinary (256)
CCNumber - Numeric(18,0)


Let's insert data in the column of the table,
Open symmetric key SK1
Decryption by certificate C1
insert into TestEncryption(Id, EncryptedCCNumber, CCNumber) values (1, ENCRYPTBYKEY(key_guid('SK1'),'5000'), '5000')

Close symmetric key SK1
Now it's time to check if the data is encrypted or not so when you execute a simple query you will get the data from the Table as it is.
select * from TestEncryption 

IF you want to DECRYPT the data you can use the below script
Open symmetric key SK1
Decryption by certificate C1
select *, convert(varchar, DECRYPTBYKEY(EncryptedCCNumber)) as 'Decrypted CC Number' from TestEncryption

Close symmetric key SK1
You will get an extra column named "Decrypted CC Number". This way we can insert/update and select the encrypted data from the table in SQL Server.

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SQL Server 2016 Hosting - HostForLIFE.eu :: About Views in SQL Server

clock March 6, 2019 10:06 by author Peter

What a View is
A view is a virtual table in the database whose contents are defined by a query.
A view appears just like a real table, with a set of named columns and rows of data. Unlike a real table, a view does not exist in the database as a stored set of data values. Instead, the rows and columns of data are generated from the query results defined by the View.

Types of Views in SQL Server
System Views

  • Information Schema View.
  • Catalog view
  • Dynamic Management View (DMV)

User Defined Views

  • Simple View
  • Complex View

create table Authors 

AuthordId int, 
AuthorName varchar(Max), 
Article varchar (Max), 
AuthorRank int 

-------Inserting Data into Authors Table---- 
Insert into Authors values (1,'Mahesh Chand','C# fundamentals',1) 
Insert into Authors values (2,'PraveenKumar','Wpf',20) 
Insert into Authors values (3,'Dhananjaykumar','windowsApplication',3) 
Insert into Authors values (4,'PinalDeve','SqlTrace',4) 
Insert into Authors values (5,'Abhinav','oops',2) 
Insert into Authors values (6,'Abhijit','WCF',5) 
Insert into Authors values (7,'Amit','DatabaseMirroring',7) 
Insert into Authors values (8,'Karthik','ssis',8) 
Insert into Authors values (9,'Divya','WebApi',9) 

(1 row(s) affected)
(1 row(s) affected)
(1 row(s) affected)


System Views

System Views are predefined Views that already exist in the Master database of SQL Server. These System Views are used as template Views for all newly created databases. These system Views will be automatically created for any user defined database.

Information Schema View
The Information Schema Views are used to display information of a database, such as tables and columns. In SQL Server there are nearly twenty different Information Schema Views.
Example: To determine the complete information of an Authors table using an Information Schema View:
---To see the detail information of Authors Table 
Select * from INFORMATION_SCHEMA.COLUMNS where TABLE_NAME='Authors' 

TABLE_CATALOG TABLE_SCHEMA TABLE_NAME COLUMN_NAME
C#Corner dbo Authors AuthordId
C#Corner dbo Authors AuthorName
C#Corner dbo Authors Article
C#Corner dbo Authors AuthorRank

Catalog view
Catalog Views are used to show database self-describing information.
Catalog views are also used to return information that is used by the SQL Database Engine like objects, logins permissions and so on.

Example:

  1. --For list of all Views in a Database  
  2. select * from sys.all_views  
  3. ---For list of tables in a database  
  4. select * from sys.tables 

Dynamic Management View (DMV)
DMVs are introduced in SQL Server 2005.
DMVs gives the database administration information about the current state of SQL Server machine on various aspects.
DMVs are easier to detect the health of SQL Server using these views.
DMVs replace many of the DBCC Commands.
All Dynamic Management Views (DMVs) exist in the sys schema and follow this naming convention dm_*.
There are two types of DMVs.

1. Server-scoped DMV
Server-scoped DMVs are Stored in Master Database.
Server-scoped DMVs are used to for the state of an entire SQL Server instance.
Server-scoped DMVs require VIEW SERVER STATE PERMISSION on the server.

2. Database-scoped DMV
Database-scoped DMVs are stored specific to each database.
Database-scoped DMVs require DATABASE STATE PERMISSION on the database.

The following are some of the Dynamic Management Views:
Sys.dm_exec_Cached_plans: Returns the information about query Execution Plans that are cached by SQL-SERVER for faster query execution.
Sys.dm_exec_Query_plan: Returns the show plan in XML format for a T-SQL batch.
Sys.dm_exec_Query_stats: Returns aggregate performance statistics for Cached Query Plans.
Sys.dm_exec_requests: Returns information about each request that is executing within SQL Server.

User Defined Views
These are the views that are defined by the user as per the their requirements.

Simple view
A simple view is one that can be addressed by DML statements as well as SELECT. As might be expected, simple views are based on relatively simple SELECT statements.
It can be used for retrieving data, as well as updating or deleting rows. Rows updated or deleted in the view are updated or deleted data in the table the view was created with. It should also be noted that as data in the original table data changes.
A simple view can be created from a single table.
A simple view does not contain functions.
A simple view does not contain a group of data.

Complex View
We use Complex Views when we want to display data from two or more tables, using a group cluase or a grouping of aggregate functions.
A Complex View can be created from one or more table.
A Complex View contains functions.
A Complex View contains a group of data,

Creating Views
We can create views in 2 ways.

  1. Through Query Designer.
  2. Through Database

Through Query Designer
Database views are created using the CREATE VIEW statement. Views can be created from a single table, multiple tables, or another view.
Syntax:
Create view view_Name
As
....Ur Query.....

Example:
Create view Authors Info

As
Select AuthorName,Article,Rank from Authors

Using SQL Server Management Studio

To create a view using the Query and View Designers:

  1. In Object Explorer, expand the database where you want to create your new view.
  2. Right-click the Views folder, then click New View.
  3. In the Add Table dialog box, select the table that you want to include in your new view from one of the following tabs: Tables, Views, Functions, and Synonyms.
  4. Click Add, then click Close.
  5. In the Query Design Pane, select the columns or other elements to include in the new view.
  6. In the Criteria Pane, select additional sort or filter criteria for the columns.
  7. On the File menu, click Save view name.
  8. In the Choose Name dialog box, enter a name for the new view and click OK.

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SQL Server 2016 Hosting - HostForLIFE.eu :: Difference Between TRUNCATE, DELETE, And DROP In SQL Server

clock February 27, 2019 11:25 by author Peter

The difference between TRUNCATE, DELETE, and DROP is one of the most common interview question. Here are some of the common differences between them.

TRUNCATE

TRUNCATE SQL query removes all rows from a table, without logging the individual row deletions.

The following example removes all data from the Customers table.

TRUNCATE TABLE Customers;  
TRUNCATE is a DDL command
TRUNCATE is executed using a table lock and whole table is locked for remove all records.
We cannot use WHERE clause with TRUNCATE.
TRUNCATE removes all rows from a table.
Minimal logging in transaction log, so it is performance wise faster.
TRUNCATE TABLE removes the data by deallocating the data pages used to store the table data and records only the page deallocations in the transaction log.
Identify column is reset to its seed value if table contains any identity column.
To use Truncate on a table you need at least ALTER permission on the table.
Truncate uses the less transaction space than Delete statement.
Truncate cannot be used with indexed views.
TRUNCATE is faster than DELETE.

DELETE
To execute a DELETE queue, delete permissions are required on the target table. If you need to use a WHERE clause in a DELETE, select permissions are required as well.

The following query deletes all rows from the Customers table. 
DELETE FROM Customers; 
GO


The following SQL query deletes all rows from the Customers table where OrderID is greater than 1000.

DELETE FROM Customers WHERE OrderId > 1000; 
GO 


DELETE is a DML command.
DELETE is executed using a row lock, each row in the table is locked for deletion.
We can use where clause with DELETE to filter & delete specific records.
The DELETE command is used to remove rows from a table based on WHERE condition.
It maintain the log, so it slower than TRUNCATE.
The DELETE statement removes rows one at a time and records an entry in the transaction log for each deleted row.
Identity of column keep DELETE retain the identity.
To use Delete you need DELETE permission on the table.
Delete uses the more transaction space than Truncate statement.
Delete can be used with indexed views.

DROP
DROP table query removes one or more table definitions and all data, indexes, triggers, constraints, and permission specifications for those tables. DROP command requires ALTER permission on the schema to which the table belongs, CONTROL permission on the table, or membership in the db_ddladmin fixed database role.

The following SQL query drops the Customers table and its data and indexes from the current database.
DROP TABLE Customers ; 

The DROP command removes a table from the database.
All the tables' rows, indexes and privileges will also be removed.
No DML triggers will be fired.
The operation cannot be rolled back.
DROP and TRUNCATE are DDL commands, whereas DELETE is a DML command.
DELETE operations can be rolled back (undone), while DROP and TRUNCATE operations cannot be rolled back

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SQL Server 2016 Hosting - HostForLIFE.eu :: TRIM Function In SQL Server 2017

clock February 20, 2019 10:22 by author Peter

With the release of SQL Server 2017, a new TRIM() is also introduced which helps to remove the white space/characters from both sides of a string. Before 2017, this functionality was achieved by using the following SQL functions.
    REPLACE - used o replace a character from a string
    LTRIM - trim the white spaces from the left side of a string
    RTRIM - trim the white spaces from the right side of a string

I can explain the functionality with two scenarios.

Let's assume, we have a string named ' ABC ' and we are going to eliminate the white spaces from both sides of the string.
 
In SQL, we usually use the LTRIM and RTRIM function like in the code below.
    SELECT LTRIM( RTRIM(' ABC ')) 

Now, this can be done by using a single TRIM function.
    SELECT TRIM(' ABC ') 

Test results from SSMS can be seen below.

Assume we have a string named 'X ABC Y' and we need to extract 'ABC' from that. As usual, we will go with the REPLACE function as follows.
    SELECT REPLACE(REPLACE('X ABC Y','X ',''),' Y','') 

Here you go with the TRIM function.
    SELECT TRIM('XY ' FROM 'X ABC Y') 

Test results from SSMS are shown below.

Note - It is necessary that you have to mention the trailing charter in the TRIM function, otherwise, this will not work as expected.
 
For example, if you try to remove the 'white space' only from the string 'X  ABC  Y', then TRIM will not help you. Similarly,  if you don't mention the letter 'Y', TRIM will not remove the white space after the string, even though you already mentioned the 'X' and the 'white space' characters inside the TRIM function. See these scenarios in the below screenshot.
 
Test results from SSMS,

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AngularJS Hosting - HostForLIFE.eu :: AES Encryption/Decryption With Angular 7

clock February 15, 2019 10:15 by author Peter

Most of the time, a developer requires encryption and decryption for encoding a message or information in such a way that only authorized person can retrieve that information.
In this article, I will discuss the implementation of AES encryption and decryption with Angular 7 while developing an application.

So, the first question that comes in our mind is "What is AES?".
AES stands for "Advanced Encryption Standard".
It is a tool that is used to encrypt and decrypt the simple text using AES encryption algorithm.
This algorithm was developed by two Belgian cryptographers, Joan Daemen and Vincent Rijmen.
AES was designed to be efficient in both, hardware and software, and supports a block length of 128 bits and key lengths of 128, 192, and 256 bits.

When to use AES Encryption

When you want to encrypt a confidential text into a decryptable format, for example - when you need to send some sensitive data in an e-mail.
The decryption of the encrypted text is possible only if you know the right password.

Now, try to implement the AES encryption and decryption in Angular 7. It's very easy to implement in Angular 7 with the help of crypto-js.

First, we create a new project with the following command.
ng new EncryptionDescryptionSample 

After that, install crypto.js file, by the following command.
npm install crypto-js --save 

For better UI, we also install bootstrap by the following command.
npm install bootstrap --save 

After running the above command, check the package.json file if it is installed or not. Your file should look like this.
AES Encryption/Decryption with Angular 7

Now, go to "app.component.html" file and replace the existing code with the below code.
<h1 class="text-center">Encrypt-Decrypt with AES</h1> 
 
<br> 
<div> 
  <div class="row"> 
    <div class="col-sm-6"> 
      <button type="button" class="btn btn-primary btn-lg btn-block"> 
        Encryption 
      </button> 
      <br> 
      <div class="form-group"> 
        <label for="txtTextToConvert">Plain Text</label> 
        <input type="text" class="form-control" placeholder="Enter text you want to encrypt" [(ngModel)]="plainText"> 
      </div> 
 
      <div class="form-group"> 
        <label for="txtPassword">Password</label> 
        <input type="password" class="form-control" placeholder="Enter encryption password" [(ngModel)]="encPassword"> 
      </div> 
      <textarea class="form-control" readonly rows="3">{{conversionEncryptOutput}}</textarea> 
      <br> 
      <button type="button" class="btn btn-success float-right" (click)="convertText('encrypt')">Encrypt</button> 
    </div> 
    <div class="col-sm-6"> 
      <button type="button" class="btn btn-dark btn-lg btn-block"> 
        Decryption 
      </button> 
      <br> 
      <div class="form-group"> 
        <label for="txtTextToConvert">Encrypted Text</label> 
        <input type="text" class="form-control" placeholder="Enter text you want to decrypt" [(ngModel)]="encryptText"> 
      </div> 
 
      <div class="form-group"> 
        <label for="txtPassword">Password</label> 
        <input type="password" class="form-control" placeholder="Enter decryption password" [(ngModel)]="decPassword"> 
      </div> 
      <textarea class="form-control" readonly rows="3">{{conversionDecryptOutput}}</textarea> 
      <br> 
      <button type="button" class="btn btn-success float-right" (click)="convertText('decrypt')">Decrypt</button> 
    </div> 
  </div> 
</div> 


Now, visit "app.component.ts" file and write the below code,
import { Component } from '@angular/core'; 
import * as CryptoJS from 'crypto-js'; 
 
@Component({ 
  selector: 'app-root', 
  templateUrl: './app.component.html', 
  styleUrls: ['./app.component.css'] 
}) 
export class AppComponent { 
  title = 'EncryptionDecryptionSample'; 
   
  plainText:string; 
  encryptText: string; 
  encPassword: string; 
  decPassword:string; 
  conversionEncryptOutput: string; 
  conversionDecryptOutput:string; 
   
  constructor() { 
  } 
  //method is used to encrypt and decrypt the text 
  convertText(conversion:string) { 
      if (conversion=="encrypt") { 
        this.conversionEncryptOutput = CryptoJS.AES.encrypt(this.plainText.trim(), this.encPassword.trim()).toString(); 
      } 
      else { 
        this.conversionDecryptOutput = CryptoJS.AES.decrypt(this.encryptText.trim(), this.decPassword.trim()).toString(CryptoJS.enc.Utf8); 
      
    } 
  } 


In the above code, we used the Encrypt method of AES and passed our plain text with a password to encrypt the string. Similarly, we used the Decrypt method of AES and passed our encrypted text with a password to decrypt the string. Be sure that both times, your password is the same. For using both of these methods, you need to import "CryptoJS" from crypto-js.
import * as CryptoJS from 'crypto-js'; 

Now, let us run the project by using the following command.
ng serve --o 

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SQL Server 2016 Hosting - HostForLIFE.eu :: Brief Introduction To Indexes In SQL Server

clock February 12, 2019 10:42 by author Peter

If you want to find a record in a table without having an index, the system will scan the whole table to get that record. Well, this is a very costly operation in terms of time. For example, if your table has 10 million records, it will scan all these records to find the value. To overcome this problem, indexes are used. Indexes use the B-TREE search algorithm to search a record in a table, which is way faster than the table scan.

Types of Index
Below are the frequently used types of Indexes.

  • Clustered Index
    A clustered index is an index that defines the physical order of records to be stored in a table. Therefore, the table can have only one clustered index. 
  • Non-Clustered Index
    A non-clustered index is similar to an index in a book. The data is stored in one place and the index is stored in another place. Here, the index has pointers to the storage location of the data. Therefore, a table can have more than one Non-clustered index. 
The syntax for creating an index.
CREATE INDEX <Index Name>  
ON <Table Name> (<Column Name>);  
  
/*Example of creating index on Lastname column of Persons table*/  
  
CREATE INDEX idx_lastname  
ON Persons (LastName); 

Benefits of indexing foreign key columns

There are two primary benefits of using the Index on foreign key.
  1. Makes delete operation of parent table faster
    When you delete a row from a parent table, the SQL Server checks if there are any rows which reference the row being deleted in the child table. To find the rows efficiently, an index on the foreign key column is extremely useful.
  2. Making joins faster
    Using Index, SQL Server can more effectively find the rows to join to when the child and parent tables are joined.

Can we have multiple indexes on the same column?

  • As you can have only one clustered index per table, you cannot have multiple clustered indexes on the same column; however, you can have multiple non-clustered indices on the same column.

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SQL Server 2016 Hosting - HostForLIFE.eu :: How to Scheduling Things To Run In SQL Server?

clock January 23, 2019 10:21 by author Peter

A key part of the SQL Server Agent is the ability to schedule jobs. While you can create one schedule for each agent job, frequently with applications like Reporting Services, users use Shared Schedules across multiple jobs. For instance, you can set a schedule to run at 8 am on week days or run every 2 hours or pick from a predefined list of schedules that already exist in the MSDB database. These are very convenient. However, if you choose to use these be sure you are keeping track of what is running for each of these shared schedules. You should not have everything running at once.

This is an example of a job schedule in a Management Studio SQL Server Agent Job. You can create a new one or pick from a list of already made schedules.

There’s nothing inherently wrong with using shared schedules—some very small operations can all run at the same time, however when you start to use them for larger operations you can really impact the overall performance of your server.

Many times, I have seen high CPU or locks as well as many other performance issues due to the system being overloaded with jobs running on shared schedules or all at the same time (midnight is a frequently common choice). Not every report to should run at 8 am and every data load run every 2 hours. If you not using shared schedules or added a separate schedule per job it is also important to make sure you are not running up against other things running. If you are using applications like SSRS, then you need to pay attention to when the report subscription refreshes are happening. Don’t overload your system by having everything run at once. Job and subscription schedules need to be analyzed and evaluated just like everything else you care for in your database.

To keep this from happening consult your agent jobs to see what other jobs are running before scheduling additional ones. You can easily get a glimpse in Job activity monitor to see what’s running and when it will run next.

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AngularJS Hosting - HostForLIFE.eu :: How to Create Cascading Dropdown in AngularJS?

clock January 16, 2019 11:50 by author Peter

In this post, I will make a Cascading Dropdown in AngularJS. Add 2 Class 1 for Countries and other for state. Write the following code:
public class Country 

    public int CountryId { get; set; } 
    public string CountryName { get; set; } 

public class State 

    public int StateId { get; set; } 
    public string StateName { get; set; } 
    public int CountryId { get; set; } 

Create a ActionResult Name it as Index [Add a View].

Add the script

<script src="~/Scripts/angular.min.js"></script> 

Create a js Name it in my case its CascadingDropdown.

var app = angular.module('myApp', []); 
app.controller('myController', function ($scope, $http) { 
    getcountries(); 
    function getcountries() { 
     
        $http({ 
            method: 'Get', 
            url: '/Home/Countries' 
 
        }).success(function (data, status, header, config) { 
 
            $scope.countries = data; 
        }).error(function (data, status, header, config) { 
            $scope.message = "Error"; 
        }); 
    } 
 
    $scope.GetStates = function ()  
    { 
        var countryIdselected = $scope.countrymodel; 
        if (countryIdselected) { 
            $http({ 
                method: 'Post', 
                url: '/Home/States', 
                data: JSON.stringify({ countryId: countryIdselected }) 
            }).success(function (data, status, header, config) { 
                $scope.states = data; 
            }).error(function (data, status, header, config) { 
                $scope.message = "Error"; 
            }) 
        } 
        else { 
            $scope.states = null; 
        } 
    } 
}); 
 
 
//Calls for Country DropDown 
 public ActionResult Countries() 
        { 
            List<Country> cobj = new List<Country>(); 
            cobj.Add(new Country { CountryId = 1, CountryName = "India" }); 
            cobj.Add(new Country { CountryId = 2, CountryName = "Srilanka" }); 
            cobj.Add(new Country { CountryId = 3, CountryName = "USA" }); 
 
            return Json(cobj, JsonRequestBehavior.AllowGet); 
        } 
 
//Calls for State DropDown with CountryID as Parameter 
 
        public ActionResult States(int countryId) 
        { 
   List<State> sobj = new List<State>(); 
   sobj.Add(new State { StateId = 1, StateName = "Karnataka", CountryId = 1 }); 
   sobj.Add(new State { StateId = 2, StateName = "Kerala", CountryId = 1 }); 
   sobj.Add(new State { StateId = 3, StateName = "TamilNadu", CountryId = 1 }); 
   sobj.Add(new State { StateId = 1, StateName = "Newyork", CountryId = 3 }); 
   sobj.Add(new State { StateId = 1, StateName = "Colombo", CountryId = 2 }); 
 
//Filter based on CountryID 
            var result = sobj.Where(x => x.CountryId == countryId).Select(x => new { x.StateId, x.StateName }); 
 
            return Json(result); 
        } 
 
//IndexView 
//  Add the script file <script src="~/Scripts/CascadingDropdown.js"></script> 
<div ng-app="myApp"> 
       
            <form name="mainForm"  ng-controller="myController"> 
 
                <select ng-model="countrymodel" ng-options=" c.CountryId as c.CountryName for c in countries" ng-change="GetStates()"> 
                    <option value="">-- Select Country --</option> 
                </select> 
                <select ng-model="statemodel" ng-options="s.StateId as s.StateName for s in states "> 
                    <option value="">-- Select State --</option> 
                </select> 
            </form> 
</div>  


I hope it works for you!

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SQL Server 2016 Hosting - HostForLIFE.eu :: ASCII Values Of Alphabets And Numbers In SQL Server

clock January 11, 2019 11:10 by author Peter

To find the ASCII value of an alphabet or a number, we can use ASCII function in SQL Server. We will see how to get the ASCII value of numbers from 0-9 and uppercase and lowercase alphabets.

What is ASCII?
ASCII (American Standard Code for Information Interchange) is the most common format for text files in computers and on the internet. In an ASCII file, each alphabetic, numeric, or special character is represented with a 7-bit binary number (a string of seven 0s or 1s). There can be 128 possible characters defined. It serves as a character encoding standard for modern computers.

Syntax
ASCII ( ‘character_expression’ )

ASCII value of capital A is 65 and Z 90.
    SELECT ASCII('A') 
    SELECT ASCII('Z') 


To find the ASCII values of alphabets from A to Z, use this code.

    DECLARE @Start int 
    set @Start=65 
    while(@Start<=90) 
    begin 
    print char(@Start) 
    set @Start=@Start+1 
    end 


To find the ASCII values of characters from a to z, we can use this query.
    SELECT ASCII('a') 
     
    SELECT ASCII('z') 
     
    DECLARE @Start int 
    set @Start=97 
    while(@Start<=122) 
    begin 
    print char(@Start) 
    set @Start=@Start+1 
    end 

ASCII Values Of Alphabets And Number In SQL Server

To find the ASCII value of numbers from 0 to 9, we can use this query.
    SELECT ASCII(9) 
     
    SELECT ASCII(0) 
     
    DECLARE @Start int 
    set @Start=48 
    while(@Start<=57) 
    begin 
    print char(@Start) 
    set @Start=@Start+1 
    end

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SQL Server 2016 Hosting - HostForLIFE.eu :: APPROX_COUNT_DISTINCT Function In SQL

clock January 7, 2019 11:13 by author Peter

Approximate COUNT DISTINCT

We all have written queries that use COUNT DISTINCT to get the unique number of non-NULL values from a table. This process can generate a noticeable performance hit especially for larger tables with millions of rows. Many times, there is no way around this. To help mitigate this overhead SQL Server 2019 introduces us to approximating the distinct count with the new APPROX_COUNT_DISTINCT function. The function approximates the count within a 2% precision to the actual answer at a fraction of the time.

Let’s see this in action.
In this example, I am using the AdventureworksDW2016CTP3 sample database which you can download here.
    SET STATISTICS IO ON 
    SELECT COUNT(DISTINCT([SalesOrderNumber])) as DISTINCTCOUNT 
    FROM [dbo].[FactResellerSalesXL_PageCompressed] 


SQL Server Execution Times
CPU time = 3828 ms, elapsed time = 14281 ms.
    SELECT APPROX_COUNT_DISTINCT ( [SalesOrderNumber]) as APPROX_DISTINCTCOUNT 
    FROM [dbo].[FactResellerSalesXL_PageCompressed] 


SQL Server Execution Times
CPU time = 7390 ms, elapsed time = 4071 ms.

APPROX_COUNT_DISTINCT Function In SQL

You can see the elapsed time is significantly lower! Great improvement using this new function.

The first time I did this, I did it wrong. A silly typo with a major result difference. So take a moment and learn from my mistake.

Note that I use COUNT(DISTINCT(SalesOrderNumber)) not DISTINCT COUNT (SalesOrderNumber ). This makes all the difference. If you do it wrong, the numbers will be way off as you can see from the below result set. You’ll also find that the APPROX_DISTINCTCOUNT will return much slower than the Distinct Count; which is not expected.

APPROX_COUNT_DISTINCT Function In SQL

Remember COUNT(DISTINCT expression) evaluates the expression for each row in a group and returns the number of unique, non-null values, which is what APPROX_COUNT_DISTINCT does. DISTINCT COUNT (expression) just returns a row count of the expression, there is nothing DISTINCT about it.

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HostForLIFE.eu is European Windows Hosting Provider which focuses on Windows Platform only. We deliver on-demand hosting solutions including Shared hosting, Reseller Hosting, Cloud Hosting, Dedicated Servers, and IT as a Service for companies of all sizes.

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