Tuesday, June 25, 2013

How to select first ‘n’ records from a table?

0 comments Posted by Rahul Kharde at 9:49 PM
The SELECT TOP clause is used to specify the number of records to return. The SELECT TOP clause can be very useful on large tables with thousands of records. Returning a large number of records can impact on performance.

Example

CREATE TABLE [dbo].[Emp]
(
      [EmpID] [int] IDENTITY(1,1) NOT NULL,
      [EmpName] [varchar](50) NULL,
)

INSERT INTO EMP(EmpName)VALUES('ABC')
INSERT INTO EMP(EmpName)VALUES('CDE')
INSERT INTO EMP(EmpName)VALUES('PQR')
INSERT INTO EMP(EmpName)VALUES('XYZ')
INSERT INTO EMP(EmpName)VALUES('NML')

 With Top Clause SELECT Top 3 Records

SELECT Top 3 * FROM Emp

Without TOP Clause 

SELECT * FROM Emp e1
WHERE (SELECT COUNT(*) FROM Emp e2 WHERE e2.EmpID<e1.EmpID)<3

Output

Emp_ID
Emp_Name
1
ABC
2
CDE
3
PQR

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Friday, June 21, 2013

Difference between STUFF and REPLACE in SQL Server?

0 comments Posted by Rahul Kharde at 2:23 AM

REPLACE is used to replace all the occurrences of the given pattern in a string.

Example

SELECT REPLACE('Hello i am here','H','m')
-- mello i am mere



STUFF used to replace the part of string with some other string.

Example
 
SELECT STUFF('Hello i am here',1,5,'Hi')
-- Hi i am here



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Thursday, June 20, 2013

What is the difference between Local and Global temporary table in SQL-server?

0 comments Posted by Rahul Kharde at 4:10 AM

Local temporary table
Global temporary table
Denoted by # symbol.
Denoted by ## symbol.
Local temporary tables are visible only to their creators during the same connection to an instance of SQL Server as when the tables were first created or referenced. Local temporary tables are deleted after the user disconnects from the instance of SQL Server.
Global temporary tables are visible to any user and any connection after they are created, and are deleted when all users that are referencing the table disconnect from the instance of SQL Server.
Tables are visible only in the current session
Tables are visible to all sessions.
Cannot be shared between multiple users.
Can be shared between multiple users.

Example

Local Temporary table

SELECT * FROM #temp

Global Temporary table

SELECT * FROM ##temp
 
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Wednesday, June 19, 2013

What is AutoEventWireup?

0 comments Posted by Rahul Kharde at 9:30 PM

The ASP.NET page framework also supports an automatic way to associate page events and methods. If the AutoEventWireup attribute of the Page directive is set to true (or if it is missing, since by default it is true), 

  • AutoEventWireup is an attribute in Page directive.  
  • AutoEventWireup is a Boolean attribute that indicates whether the ASP.NET pages events are auto-wired. 
  • AutoEventWireup will have a value true or false. By default it is true.

<%@ Page Language="C#" AutoEventWireup="true" CodeBehind="Default.aspx.cs" Inherits="WebApplication2._Default" %>


the page framework calls page events automatically, specifically the Page_Init and Page_Load methods. In that case, no explicit Handles clause or delegate is needed.

Example 1

With AutoEventWireup="true"

HTML Code

<%@ Page Language="C#" AutoEventWireup="true" CodeBehind="Default.aspx.cs" Inherits="WebApplication2._Default" %>

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">

<html xmlns="http://www.w3.org/1999/xhtml" >
<head runat="server">
    <title>Untitled Page</title>
</head>
<body>
    <form id="form1" runat="server">
    <div>
   
        <asp:Button ID="Button1" runat="server" onclick="Button1_Click" Text="Button" />
   
    </div>
    </form>
</body>
</html>

Code

protected void Page_Load(object sender, EventArgs e)
{
    Response.Write("IN");
}

protected void Button1_Click(object sender, EventArgs e)
{
    Response.Write("<br>Button Click");
}

When we click Button then both page load and button click event get fired.

OUTPUT

IN
Button Click





Example 2

With  AutoEventWireup="false"

Now set the AutoEventWireup propoerty false

<%@ Page Language="C#" AutoEventWireup="false" CodeBehind="Default.aspx.cs" Inherits="WebApplication2._Default" %>

Again click the Button Event this time only click event get fired.

OUTPUT

Button Click


Why my ASP.NET events fire twice?

A very common question asked. The simple answer to this question is:

If you have AutoEventWireup="true" as well as you also have defined delegates for the event handling in your code, .NET Framework will automatically call methods based on their names and also the methods you defined explicitly.


Disadvantages of AutoEventWireup attribute
  1. AutoEventWireup uses fixed naming convention for the events. Page events handlers have specific predictable names. This limits your flexibility in how you name event handlers.
  2. If you do set AutoEventWireup to true, Visual Studio will generate code to bind the events and the page framework will automatically call events based on their names. This can result in the same event code being called twice when the page runs. As a consequence, you should always leave AutoEventWireup set to false when working in Visual Studio.
  3. Another disadvantage is that performance is adversely affected, because ASP.NET searches for methods at run-time. For a Web site with high traffic volumes, the impact on performance could be significant.

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