Thursday, October 20, 2011

Difference between Primary key and Unique Key with example

4 comments Posted by Rahul Kharde at 11:01 PM
PRIMARY KEY AND UNIQUE KEY are similar except it has different functions. Primary key makes the table row unique (i.e, there cannot be 2 row with the exact same key). You can only have 1 primary key in a database table.

Unique key makes the table column in a table row unique (i.e., no 2 table row may have the same exact value). You can have more than 1 unique key table column (unlike primary key which means only 1 table column in the table is unique).

Primary Key
Unique Key
It will not accept null values
One and only one Null values are accepted.
There will be only one primary key in a table
More than one unique key will be there in a table.
Clustered index is created in Primary key
Non-Clustered index is created in unique key.
Primary key allows each row in a table to be uniquely identified and ensures that no duplicate rows exist.
Unique key constraint is used to prevent the duplication of key values within the rows of a table and allow null values.

Example

CREATE TABLE BOOK
(
    BOOKID INT NOT NULL PRIMARY KEY,
    BOOKName VARCHAR(100)
)
GO

ALTER TABLE BOOK ADD CONSTRAINT UK_BookName UNIQUE(BOOKName)
GO

INSERT INTO BOOK(BOOKID,BOOKName)VALUES(1,null)

INSERT INTO BOOK(BOOKID,BOOKName)VALUES(2,'ASP')

INSERT INTO BOOK(BOOKID,BOOKName)VALUES(3,'C')

INSERT INTO BOOK(BOOKID,BOOKName)VALUES(4,'C++')

INSERT INTO BOOK(BOOKID,BOOKName)VALUES(5,'PHP')


BOOKID
BOOKName
1
NULL
2
ASP
3
C
4
C++
5
PHP

If you try again to insert null value into table it shows an error message

INSERT INTO BOOK(BOOKID,BOOKName)VALUES(6,null)

Cannot insert the value NULL into column 'BOOKName', table 'Testing.dbo.BOOK'; column does not allow nulls. INSERT fails.

The statement has been terminated.
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Wednesday, October 19, 2011

Page Hit Counter using the Application in ASP.NET

8 comments Posted by Rahul Kharde at 9:36 PM
It is sometimes useful to display the number of visits a page on a Web site has experienced using a counter that's displayed as part of the page's content. This is a very simple hit counter / page counter to see how many people have visited a web page if you want to show it on a web page. This is a simple using the Application in ASP.NET

Application Object

The Application object is used to store and access variables from any page, just like the Session object. The difference is that ALL users share ONE Application object (with Sessions there is ONE Session object for EACH user).
The Application object holds information that will be used by many pages in the application (like database connection information). The information can be accessed from any page. The information can also be changed in one place, and the changes will automatically be reflected on all pages.
Global.aspx
The global.asax file is used to add application level logic & processing. Note that the global.asax does not handle any UI related processing, nor does it process individual page level requests. It basically controls the following events...
Application_Start
Application_End
Session_Start
Session_End

When an web page load, this event occurs only one time in an application’s life cycle. It occurs again when you restart the IIS. When IIS reset then application count also reset to zero (0). It’s the best place to count number of visitors. 


 void Application_Start(object sender, EventArgs e)
        {
            // Code that runs on application startup
            Application["hit"] = 0;
        }

HTML

Used label to show the no of hit in web page



<html xmlns="http://www.w3.org/1999/xhtml">
<head id="Head1" runat="server">
    <title>Untitled Page</title>
</head>
<body>
    <form id="form1" runat="server">
    <div>
        <asp:Label ID="Label1" runat="server" Text="Label"></asp:Label>
    </div>
    </form>
</body>
</html>



Code



        protected void Page_Load(object sender, EventArgs e)
        {
            if (!IsPostBack)
            {
                Application["hit"] = Convert.ToInt32(Application["hit"].ToString()) + 1;
            }
            Label1.Text = "Count = " + Convert.ToInt32(Application["hit"].ToString());
        }




Download



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