HTTP Request Processing in IIS 7

IIS 7 has a similar HTTP request-processing flow as IIS 6.0. The diagrams in this section provide an overview of an HTTP request in process.

The following list describes the request-processing flow that is shown in Figure 1:

1.    When a client browser initiates an HTTP request for a resource on the Web server, HTTP.sys
        intercepts   the request.
2.    HTTP.sys contacts WAS to obtain information from the configuration store.
3.    WAS requests configuration information from the configuration store, applicationHost.config.
4.    WWW Service receives configuration information, such as application pool and site configuration.
5.    WWW Service uses the configuration information to configure HTTP.sys.
6.    WAS starts a worker process for the application pool to which the request was made.
7.    The worker process processes the request and returns a response to HTTP.sys.
8.    The client receives a response.

In a worker process, an HTTP request passes through several ordered steps, called events, in the Web Server Core. At each event, a native module processes part of the request, such as authenticating the user or adding information to the event log. If a request requires a managed module, the native ManagedEngine module creates an AppDomain, where the managed module can perform the necessary processing, such as authenticating a user with Forms authentication. When the request passes through all of the events in the Web Server Core, the response is returned to HTTP.sys. Figure 2, below, shows an HTTP request entering the worker process.

Yeild

One interesting new feature of the C# 2.0 is the "yield" keyword.  Basically it is used to iterate through objects returned by a method. It creates a state engine in IL so you can create methods that retain their state and dont have to go through the pain of maintaining state in your code.

Here is a simple example that demonstrates how yield return can be used to maintain state in a method. Every time you call  GetInt() you will receive a new incremented integer.
public static IEnumerable GetInt()
{
   for (int i = 0; i < 5; i++)
       yield return i;
}

Here's the implementation.

public partial class Yield : System.Web.UI.Page
{
    protected void Page_Load(object sender, EventArgs e)
    {
        foreach (int i in GetInt())
            Response.Write(i.ToString());
    }

    public static IEnumerable GetInt()
    {
          for (int i = 0; i < 5; i++)
            yield return i;
    }
}
Here  is the difference  on the execution

Typical Implementation                                  Yield Implementation 

Caller calls function                                            Caller calls function
Function executes and returns list                       Caller requests item
Caller uses list                                                    Next item returned
                                                                          Goto step #2


Although the execution of the yield implementation is a little more complicated, what we end up with is an implementation that "pulls" items one at a time instead of having to build an entire list before returning to the client.


Usually, the "yield" keyword will be useful when you implement the GetEnumerator() method of the IEnumerable interface
After all the Yield is creating addional overhead and use when required exactly.

const vs. readonly

const and readonly perform a similar function on data members, but they have a few important differences.
const

A constant member is defined at compile time and cannot be changed at runtime. Constants are declared as a field, using the const keyword and must be initialized as they are declared. For example;

    public class MyClass
           {
               public const double PI = 3.14159;
           }

PI cannot be changed in the application anywhere else in the code as this will cause a compiler error.

Constants must be a value type (sbyte, byte, short, ushort, int, uint, long, ulong, char, float, double, decimal, or bool), an enumeration, a string literal, or a reference to null.

Since classes or structures are initialized at run time with the new keyword, and not at compile time, you can't set a constant to a class or structure.

Constants can be marked as public, private, protected, internal, or protected internal.

Constants are accessed as if they were static fields, although they cannot use the static keyword.

To use a constant outside of the class that it is declared in, you must fully qualify it using the class name.

readonly

A read only member is like a constant in that it represents an unchanging value. The difference is that a readonly member can be initialized at runtime, in a constructor as well being able to be initialized as they are declared. For example:

          public class MyClass
            {
               public readonly double PI = 3.14159;
            }

           or

          public class MyClass
            {
              public readonly double PI;

              public MyClass()
               {
                 PI = 3.14159;
               }
             }

Because a readonly field can be initialized either at the declaration or in a constructor, readonly fields can have different values depending on the constructor used. A readonly field can also be used for runtime constants as in the following example:

public static readonly uint l1 = (uint)DateTime.Now.Ticks;

    * readonly members are not implicitly static, and therefore the static keyword can be applied to a readonly  field explicitly if required.

    * A readonly member can hold a complex object by using the new keyword at initialization.

    * readonly members cannot hold enumerations.

static

Use of the static modifier to declare a static member, means that the member is no longer tied to a specific object. This means that the member can be accessed without creating an instance of the class. Only one copy of static fields and events exists, and static methods and properties can only access static fields and static events. For example:

          public class Car
             {
               public static int NumberOfWheels = 4;
             }

The static modifier can be used with classes, fields, methods, properties, operators, events and constructors, but cannot be used with indexers, destructors, or types other than classes.

static members are initialized before the static member is accessed for the first time, and before the static constructor, if any is called. To access a static class member, use the name of the class instead of a variable name to specify the location of the member. For example:

            int i = Car.NumberOfWheels;

System.Web Element

Specifies the root element for the ASP.NET configuration section and contains configuration elements that configure ASP.NET Web applications and control how the applications behave.

<system.web> 
   <anonymousIdentification> 
   <authentication> 
   <authorization> 
   <browserCaps> 
   <caching> 
   <clientTarget> 
   <compilation> 
   <customErrors> 
   <deployment> 
   <deviceFilters> 
   <globalization> 
   <healthMonitoring> 
   <hostingEnvironment> 
   <httpCookies> 
   <httpHandlers> 
   <httpModules> 
   <httpRuntime> 
   <identity> 
   <machineKey> 
   <membership> 
   <mobileControls> 
   <pages> 
   <processModel> 
   <profile> 
   <roleManager> 
   <securityPolicy> 
   <sessionPageState> 
   <sessionState> 
   <siteMap> 
   <trace> 
   <trust> 
   <urlMappings> 
   <webControls> 
   <webParts> 
   <webServices> 
   <xhtmlConformance> 
</system.web>

Element	Description
anonymousIdentification Element (ASP.NET Settings Schema)	Configures anonymous identification for application authorization. This is required to identify entities that are not authenticated when authorization is required.
authentication Element (ASP.NET Settings Schema)	Configures ASP.NET authentication support.
authorization Element (ASP.NET Settings Schema)	Configures ASP.NET authorization support.
browserCaps Element (ASP.NET Settings Schema)	Configures the settings for the browser capabilities component.
caching Element (ASP.NET Settings Schema)	Configures the cache settings for a Web application.
clientTarget Element (ASP.NET Settings Schema)	Adds aliases for specific user agents to an internal collection of user agent aliases.
compilation Element (ASP.NET Settings Schema)	Contains all compilation settings that are used by ASP.NET.
customErrors Element (ASP.NET Settings Schema)	Defines custom error messages for an ASP.NET application.
deployment Element (ASP.NET Settings Schema)	Defines configuration settings that are used to support the deployment of a Web application.
deviceFilters Element (ASP.NET Settings Schema)	Specifies a device or a device class in the ASP.NET MobileCapabilities class based on the user agent or browser. A page or application developer can use a device filter to override control properties or to define blocks of content or templates to change layout and appearance.
globalization Element (ASP.NET Settings Schema)	Configures the globalization settings of an application.
healthMonitoring Element (ASP.NET Settings Schema)	Configures an application for health monitoring.
hostingEnvironment Element (ASP.NET Settings Schema)	Defines configuration settings that control the behavior of the application hosting environment.
httpCookies Element (ASP.NET Settings Schema)	Configures properties for cookies that are used by a Web application.
httpHandlers Element (ASP.NET Settings Schema)	Maps incoming URL requests to IHttpHandler classes.
httpModules Element (ASP.NET Settings Schema)	Adds, removes, or clears HTTP modules within an application.
httpRuntime Element (ASP.NET Settings Schema)	Configures ASP.NET HTTP run-time settings. This section can be declared at the machine, site, application, or subdirectory level.
identity Element (ASP.NET Settings Schema)	Controls the application identity of the Web application.
machineKey Element (ASP.NET Settings Schema)	Configures keys to use for encryption and decryption of Forms authentication cookie data. This section allows you to configure a validation key that performs message authentication checks on view-state data and Forms authentication tickets. This section can be declared at the machine, site, or application levels but not at the subdirectory level.
membership Element (ASP.NET Settings Schema)	Configures parameters for managing and authenticating user accounts for ASP.NET membership.
mobileControls Element (ASP.NET Settings Schema)	Defines adapter sets that map ASP.NET mobile controls to corresponding adapters within the system.web section of the Web.config file.
pages Element (ASP.NET Settings Schema)	Identifies page-specific configuration settings.
processModel Element (ASP.NET Settings Schema)	Configures the ASP.NET process model settings on Internet Information Services (IIS) Web server systems.
profile Element (ASP.NET Settings Schema)	Configures parameters for managing user values by using the ASP.NET profile.
roleManager Element (ASP.NET Settings Schema)	Configures an application for role management. This element is new in the .NET Framework version 2.0.
securityPolicy Element (ASP.NET Settings Schema)	Defines valid mappings of named security levels to policy files. This section can be declared at the machine, site, or application levels.
sessionPageState Element (ASP.NET Settings Schema)	Configures page view-state settings for an ASP.NET application.
sessionState Element (ASP.NET Settings Schema)	Configures the session-state module.
siteMap Element (ASP.NET Settings Schema)	Configures the navigation infrastructure support for configuring, storing, and rendering site navigation.
trace Element (ASP.NET Settings Schema)	Configures the ASP.NET trace service.
trust Element (ASP.NET Settings Schema)	Configures the code access security permission set that is used to run a particular application. This section can be declared at the machine, site, and application levels.
urlMappings Element (ASP.NET Settings Schema)	Defines a mapping that hides the real URL and maps it to a more user friendly URL.
webControls Element (ASP.NET Settings Schema)	Specifies the shared location of the client script files.
webParts	Specifies a Web Parts personalization provider, sets personalization authorizations, and adds custom classes that extend the WebPartTransformer class for use by Web Parts connections.
webServices Element (ASP.NET Settings Schema)	Controls the settings of XML Web services that are created using ASP.NET.
xhtmlConformance Element (ASP.NET Settings Schema)	Configures XHTML 1.0–conforming control rendering.

Generics

If the operations performed by several overloaded methods are identical for each argument type, the overloaded methods can be more compactly and conveniently coded using a generic method. You can write a single generic method declaration that can be called at different times with arguments of different types. Based on the types of the arguments passed to the generic method, the compiler handles each method call appropriately.

public T Max <T>(T val1, T val2) where T : IComparable  {
    T retVal = val2;
    if (val2.CompareTo(val1) < 0)
        retVal = val1;
    return retVal;
}

And the Calling Would be like :

double doubleMax = Max <double>(3939.99, 39999.99);
int intMax = Max <int>(339, 23);
string stringMax = Max <string>("AAAA", "BBBBBB");

You can use generics in classes and in structs. Here is a useful generic point struct:

public struct Point <T>
{
   
   public T X;
   
   public T Y;
}

You can use the generic point for integer coordinates, for example:

Point <int> point;
point.X = 1;
point.Y = 2;

Or for charting coordinates that require floating point precision:

Point <double> point;
point.X = 1.2;
point.Y = 3.4;

Inheritance and Generics

When deriving from a generic base class, you must provide a type argument instead of the base-class's generic type parameter:

public class BaseClass <T>
{...}
public class SubClass : BaseClass <int>
{...}

If the subclass is generic, instead of a concrete type argument, you can use the subclass generic type parameter as the specified type for the generic base class:

public class SubClass <T> : BaseClass <T> 
{...}

When using the subclass generic type parameters, you must repeat any constraints stipulated at the base class level at the subclass level. For example, derivation constraint:

public class BaseClass <T>  where T : ISomeInterface 
{...}
public class SubClass <T> : BaseClass <T> where T : ISomeInterface
{...}

Or constructor constraint:

public class BaseClass <T>  where T : new()
{   
   public T SomeMethod()
   {
      return new T();
   }
}
public class SubClass <T> : BaseClass <T> where T : new() 
{...}

A base class can define virtual methods whose signatures use generic type parameters. When overriding them, the subclass must provide the corresponding types in the method signatures:

public class BaseClass <T>
{ 
   public virtual T SomeMethod()
   {...}
}
public class SubClass: BaseClass <int>
{ 
   public override int SomeMethod()
   {...}
}

If the subclass is generic it can also use its own generic type parameters for the override:

public class SubClass <T>: BaseClass <T>
{ 
   public override T SomeMethod()
   {...}
}

You can define generic interfaces, generic abstract classes, and even generic abstract methods. These types behave like any other generic base type:

public interface ISomeInterface <T>
{
   T SomeMethod(T t);
}
public abstract class BaseClass <T>
{
   public abstract T SomeMethod(T t);
}

public class SubClass <T> : BaseClass <T>
{
   public override T SomeMethod(T t) 
   {...)
}

There is an interesting use for generic abstract methods and generic interfaces. In C# 2.0, it is impossible to use operators such as + or += on generic type parameters. For example, the following code does not compile because C# 2.0 does not have operator constraints:

public class Calculator <T>
{
   public T Add(T arg1,T arg2)
   {
      return arg1 + arg2;//Does not compile 
   }
   //Rest of the methods 
}

Nonetheless, you can compensate using abstract methods (or preferably interfaces) by defining generic operations. Since an abstract method cannot have any code in it, you can specify the generic operations at the base class level, and provide a concrete type and implementation at the subclass level:

public abstract class BaseCalculator <T>
{
   public abstract T Add(T arg1,T arg2);
   public abstract T Subtract(T arg1,T arg2);
   public abstract T Divide(T arg1,T arg2);
   public abstract T Multiply(T arg1,T arg2);
}
public class MyCalculator : BaseCalculator <int>
{
   public override int Add(int arg1, int arg2)
   {
      return arg1 + arg2;
   }
   //Rest of the methods 
} 

A generic interface will yield a somewhat cleaner solution as well:

public interface ICalculator <T>
{
   T Add(T arg1,T arg2);
   //Rest of the methods 
}
public class MyCalculator : ICalculator <int>
{
   public int Add(int arg1, int arg2)
   {
      return arg1 + arg2;
   }
   //Rest of the methods 
}

Extension methods

Extension methods enable you to "add" methods to existing types without creating a new derived type, recompiling, or otherwise modifying the original type. Extension methods are a special kind of static method, but they are called as if they were instance methods on the extended type. For client code written in C# and Visual Basic, there is no apparent difference between calling an extension method and the methods that are actually defined in a type.

The most common extension methods are the LINQ standard query operators that add query functionality to the existing System.Collections.IEnumerable and System.Collections.Generic.IEnumerable types. To use the standard query operators, first bring them into scope with a using System.Linq directive. Then any type that implements IEnumerable appears to have instance methods such as GroupBy, OrderBy, Average, and so on. You can see these additional methods in IntelliSense statement completion when you type "dot" after an instance of an IEnumerable type such as List or Array.

Extension methods are defined as static methods but are called by using instance method syntax. Their first parameter specifies which type the method operates on, and the parameter is preceded by the this modifier. Extension methods are only in scope when you explicitly import the namespace into your source code with a using directive.

The following example shows an extension method defined for the System.String class. Note that it is defined inside a non-nested, non-generic static class:

namespace ExtensionMethods
{
    public static class MyExtensions
    {
        public static int WordCount(this String str)
        {
            return str.Split(new char[] { ' ', '.', '?' }, StringSplitOptions.RemoveEmptyEntries).Length;
        }
    }   
}

The WordCount extension method can be brought into scope with this using directive:

using ExtensionMethods;


And it can be called from an application by using this syntax:

string s = "Hello Extension Methods";
int i = s.WordCount();

What is Yield

This is one of the new addition to C# 2.0. The meaning of this keyword is to instruct the program to run and generate the list until all the loop execution is exhausted. Thus it creates a list of items for which the predicate function returns true.

Cast() VS OfType()

Fundamentally, Cast() is implemented like this:

public IEnumerable Cast(this IEnumerable source)
{
  foreach(object o in source)
    yield return (T) o;
}

Using an explicit cast performs well, but will result in an InvalidCastException if the cast fails.
A less efficient yet useful variation on this idea is OfType():

public IEnumerable OfType(this IEnumerable source)
{
  foreach(object o in source)
    if(o is T)
      yield return (T) o;
}

The returned enumeration will only include elements that can safely be cast to the specified type.

Sql Basic Understandings

What is RDBMS?

Relational Data Base Management Systems (RDBMS) are database management systems that maintain
data records and indices in tables. Relationships may be created and maintained across and among the
data and tables. In a relational database, relationships between data items are expressed by means of
tables. Interdependencies among these tables are expressed by data values rather than by pointers.
This allows a high degree of data independence. An RDBMS has the capability to recombine the data
items from different files, providing powerful tools for data usage.

What is normalization?

Database normalization is a data design and organization process applied to data structures based on
rules that help build relational databases. In relational database design, the process of organizing data
to minimize redundancy. Normalization usually involves dividing a database into two or more tables and
defining relationships between the tables. The objective is to isolate data so that additions, deletions,
and modifications of a field can be made in just one table and then propagated through the rest of the
database via the defined relationships.

What are different normalization forms?

1NF: Eliminate Repeating Groups
Make a separate table for each set of related attributes, and give each table a primary key. Each field
contains at most one value from its attribute domain.
2NF: Eliminate Redundant Data
If an attribute depends on only part of a multi-valued key, remove it to a separate table.
3NF: Eliminate Columns Not Dependent On Key
If attributes do not contribute to a description of the key, remove them to a separate table. All
attributes must be directly dependent on the primary key
BCNF: Boyce-Codd Normal Form
If there are non-trivial dependencies between candidate key attributes, separate them out into distinct
tables.
4NF: Isolate Independent Multiple Relationships
No table may contain two or more 1:n or n:m relationships that are not directly related.
5NF: Isolate Semantically Related Multiple Relationships
There may be practical constrains on information that justify separating logically related many-to-many
relationships.
ONF: Optimal Normal Form
A model limited to only simple (elemental) facts, as expressed in Object Role Model notation.
DKNF: Domain-Key Normal Form
A model free from all modification anomalies.
Remember, these normalization guidelines are cumulative. For a database to be in 3NF, it must first
fulfill all the criteria of a 2NF and 1NF database.

What is Stored Procedure?

A stored procedure is a named group of SQL statements that have been previously created and stored
in the server database. Stored procedures accept input parameters so that a single procedure can be
used over the network by several clients using different input data. And when the procedure is
modified, all clients automatically get the new version. Stored procedures reduce network traffic and
improve performance. Stored procedures can be used to help ensure the integrity of the database.
e.g. sp_helpdb, sp_renamedb, sp_depends etc.

What is Trigger?

A trigger is a SQL procedure that initiates an action when an event (INSERT, DELETE or UPDATE)
occurs. Triggers are stored in and managed by the DBMS.Triggers are used to maintain the referential
integrity of data by changing the data in a systematic fashion. A trigger cannot be called or executed;
the DBMS automatically fires the trigger as a result of a data modification to the associated table.
Triggers can be viewed as similar to stored procedures in that both consist of procedural logic that is
stored at the database level. Stored procedures, however, are not event-drive and are not attached to a
specific table as triggers are. Stored procedures are explicitly executed by invoking a CALL to the
procedure while triggers are implicitly executed. In addition, triggers can also execute stored
procedures.
Nested Trigger: A trigger can also contain INSERT, UPDATE and DELETE logic within itself, so when the
trigger is fired because of data modification it can also cause another data modification, thereby firing
another trigger. A trigger that contains data modification logic within itself is called a nested trigger.

What is View?

A simple view can be thought of as a subset of a table. 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 in the table the
view was created with. It should also be noted that as data in the original table changes, so does data
in the view, as views are the way to look at part of the original table. The results of using a view are
not permanently stored in the database. The data accessed through a view is actually constructed using
standard T-SQL select command and can come from one to many different base tables or even other
views.

What is Index?

An index is a physical structure containing pointers to the data. Indices are created in an existing table
to locate rows more quickly and efficiently. It is possible to create an index on one or more columns of
a table, and each index is given a name. The users cannot see the indexes, they are just used to speed
up queries. Effective indexes are one of the best ways to improve performance in a database
application. A table scan happens when there is no index available to help a query. In a table scan SQL
Server examines every row in the table to satisfy the query results. Table scans are sometimes
unavoidable, but on large tables, scans have a terrific impact on performance.
Clustered indexes define the physical sorting of a database table’s rows in the storage media. For this
reason, each database table may have only one clustered index.
Non-clustered indexes are created outside of the database table and contain a sorted list of references
to the table itself.

What is the difference between clustered and a non-clustered index?

A clustered index is a special type of index that reorders the way records in the table are physically
stored. Therefore table can have only one clustered index. The leaf nodes of a clustered index contain
the data pages.
A nonclustered index is a special type of index in which the logical order of the index does not match
the physical stored order of the rows on disk. The leaf node of a nonclustered index does not consist of
the data pages. Instead, the leaf nodes contain index rows.

What are the different index configurations a table can have?

A table can have one of the following index configurations:
No indexes
A clustered index
A clustered index and many nonclustered indexes
A nonclustered index
Many nonclustered indexes

What is cursors?

Cursor is a database object used by applications to manipulate data in a set on a row-by-row basis,
instead of the typical SQL commands that operate on all the rows in the set at one time.
In order to work with a cursor we need to perform some steps in the following order:
Declare cursor
Open cursor
Fetch row from the cursor
Process fetched row
Close cursor
Deallocate cursor

What is the use of DBCC commands?

DBCC stands for database consistency checker. We use these commands to check the consistency of
the databases, i.e., maintenance, validation task and status checks.
E.g. DBCC CHECKDB - Ensures that tables in the db and the indexes are correctly linked.
DBCC CHECKALLOC - To check that all pages in a db are correctly allocated.
DBCC CHECKFILEGROUP - Checks all tables file group for any damage.

What is a Linked Server?

Linked Servers is a concept in SQL Server by which we can add other SQL Server to a Group and query
both the SQL Server dbs using T-SQL Statements. With a linked server, you can create very clean, easy
to follow, SQL statements that allow remote data to be retrieved, joined and combined with local data.
Storped Procedure sp_addlinkedserver, sp_addlinkedsrvlogin will be used add new Linked Server.

What is Collation?

Collation refers to a set of rules that determine how data is sorted and compared. Character data is
sorted using rules that define the correct character sequence, with options for specifying case-
sensitivity, accent marks, kana character types and character width.

What are different type of Collation Sensitivity?

Case sensitivity
A and a, B and b, etc.
Accent sensitivity
a and á, o and ó, etc.
Kana Sensitivity
When Japanese kana characters Hiragana and Katakana are treated differently, it is called Kana
sensitive.
Width sensitivity
When a single-byte character (half-width) and the same character when represented as a double-byte
character (full-width) are treated differently then it is width sensitive.
What's the difference between a primary key and a unique key?
Both primary key and unique enforce uniqueness of the column on which they are defined. But by
default primary key creates a clustered index on the column, where are unique creates a nonclustered
index by default. Another major difference is that, primary key doesn't allow NULLs, but unique key
allows one NULL only.

How to implement one-to-one, one-to-many and many-to-many relationships while
designing tables?

One-to-One relationship can be implemented as a single table and rarely as two tables with primary
and foreign key relationships.
One-to-Many relationships are implemented by splitting the data into two tables with primary key and
foreign key relationships.
Many-to-Many relationships are implemented using a junction table with the keys from both the tables
forming the composite primary key of the junction table.

What is a NOLOCK?


Using the NOLOCK query optimiser hint is generally considered good practice in order to improve
concurrency on a busy system. When the NOLOCK hint is included in a SELECT statement, no locks are
taken when data is read. The result is a Dirty Read, which means that another process could be
updating the data at the exact time you are reading it. There are no guarantees that your query will
retrieve the most recent data. The advantage to performance is that your reading of data will not block
updates from taking place, and updates will not block your reading of data. SELECT statements take
Shared (Read) locks. This means that multiple SELECT statements are allowed simultaneous access, but
other processes are blocked from modifying the data. The updates will queue until all the reads have
completed, and reads requested after the update will wait for the updates to complete. The result to
your system is delay(blocking).

What is difference between DELETE & TRUNCATE commands?

Delete command removes the rows from a table based on the condition that we provide with a WHERE
clause. Truncate will actually remove all the rows from a table and there will be no data in the table
after we run the truncate command.
TRUNCATE
TRUNCATE is faster and uses fewer system and transaction log resources than DELETE.
TRUNCATE removes the data by deallocating the data pages used to store the table’s data, and only the
page deallocations are recorded in the transaction log.
TRUNCATE removes all rows from a table, but the table structure and its columns, constraints, indexes
and so on remain. The counter used by an identity for new rows is reset to the seed for the column.
You cannot use TRUNCATE TABLE on a table referenced by a FOREIGN KEY constraint.
Because TRUNCATE TABLE is not logged, it cannot activate a trigger.
TRUNCATE can not be Rolled back.
TRUNCATE is DDL Command.
TRUNCATE Resets identity of the table.
DELETE
DELETE removes rows one at a time and records an entry in the transaction log for each deleted row.
If you want to retain the identity counter, use DELETE instead. If you want to remove table definition
and its data, use the DROP TABLE statement.
DELETE Can be used with or without a WHERE clause
DELETE Activates Triggers.
DELETE Can be Rolled back.
DELETE is DML Command.
DELETE does not reset identity of the table.

Difference between Function and Stored Procedure?

UDF can be used in the SQL statements anywhere in the WHERE/HAVING/SELECT section where as
Stored procedures cannot be.
UDFs that return tables can be treated as another rowset. This can be used in JOINs with other tables.
Inline UDF's can be though of as views that take parameters and can be used in JOINs and other
Rowset operations.

When is the use of UPDATE_STATISTICS command?

This command is basically used when a large processing of data has occurred. If a large amount of
deletions any modification or Bulk Copy into the tables has occurred, it has to update the indexes to
take these changes into account. UPDATE_STATISTICS updates the indexes on these tables
accordingly.

What types of Joins are possible with Sql Server?

Joins are used in queries to explain how different tables are related. Joins also let you select data from
a table depending upon data from another table.
Types of joins: INNER JOINs, OUTER JOINs, CROSS JOINs. OUTER JOINs are further classified as LEFT
OUTER JOINS, RIGHT OUTER JOINS and FULL OUTER JOINS.

What is the difference between a HAVING CLAUSE and a WHERE CLAUSE?

Specifies a search condition for a group or an aggregate. HAVING can be used only with the SELECT
statement. HAVING is typically used in a GROUP BY clause. When GROUP BY is not used, HAVING
behaves like a WHERE clause. Having Clause is basically used only with the GROUP BY function in a
query. WHERE Clause is applied to each row before they are part of the GROUP BY function in a query.

What is sub-query? Explain properties of sub-query.

Sub-queries are often referred to as sub-selects, as they allow a SELECT statement to be executed
arbitrarily within the body of another SQL statement. A sub-query is executed by enclosing it in a set of
parentheses. Sub-queries are generally used to return a single row as an atomic value, though they
may be used to compare values against multiple rows with the IN keyword.
A subquery is a SELECT statement that is nested within another T-SQL statement. A subquery SELECT
statement if executed independently of the T-SQL statement, in which it is nested, will return a result
set. Meaning a subquery SELECT statement can standalone and is not depended on the statement in
which it is nested. A subquery SELECT statement can return any number of values, and can be found
in, the column list of a SELECT statement, a FROM, GROUP BY, HAVING, and/or ORDER BY clauses of a
T-SQL statement. A Subquery can also be used as a parameter to a function call. Basically a subquery
can be used anywhere an expression can be used.
Properties of Sub-Query
A subquery must be enclosed in the parenthesis.
A subquery must be put in the right hand of the comparison operator, and
A subquery cannot contain a ORDER-BY clause.
A query can contain more than one sub-queries.

What are types of sub-queries?

Single-row subquery, where the subquery returns only one row.
Multiple-row subquery, where the subquery returns multiple rows,.and
Multiple column subquery, where the subquery returns multiple columns.

What is SQL Profiler?

SQL Profiler is a graphical tool that allows system administrators to monitor events in an instance of
Microsoft SQL Server. You can capture and save data about each event to a file or SQL Server table to
analyze later. For example, you can monitor a production environment to see which stored procedures
are hampering performance by executing too slowly.
Use SQL Profiler to monitor only the events in which you are interested. If traces are becoming too
large, you can filter them based on the information you want, so that only a subset of the event data is
collected. Monitoring too many events adds overhead to the server and the monitoring process and can
cause the trace file or trace table to grow very large, especially when the monitoring process takes
place over a long period of time.

What is User Defined Functions?

User-Defined Functions allow to define its own T-SQL functions that can accept 0 or more parameters
and return a single scalar data value or a table data type.

What kind of User-Defined Functions can be created?

There are three types of User-Defined functions in SQL Server 2000 and they are Scalar, Inline Table-
Valued and Multi-statement Table-valued.
Scalar User-Defined Function
A Scalar user-defined function returns one of the scalar data types. Text, ntext, image and timestamp
data types are not supported. These are the type of user-defined functions that most developers are
used to in other programming languages. You pass in 0 to many parameters and you get a return
value.
Inline Table-Value User-Defined Function
An Inline Table-Value user-defined function returns a table data type and is an exceptional alternative
to a view as the user-defined function can pass parameters into a T-SQL select command and in
essence provide us with a parameterized, non-updateable view of the underlying tables.
Multi-statement Table-Value User-Defined Function
A Multi-Statement Table-Value user-defined function returns a table and is also an exceptional
alternative to a view as the function can support multiple T-SQL statements to build the final result
where the view is limited to a single SELECT statement. Also, the ability to pass parameters into a T-
SQL select command or a group of them gives us the capability to in essence create a parameterized,
non-updateable view of the data in the underlying tables. Within the create function command you
must define the table structure that is being returned. After creating this type of user-defined function,
It can be used in the FROM clause of a T-SQL command unlike the behavior found when using a stored
procedure which can also return record sets.

Which TCP/IP port does SQL Server run on? How can it be changed?

SQL Server runs on port 1433. It can be changed from the Network Utility TCP/IP properties –> Port
number.both on client and the server.

What are the authentication modes in SQL Server? How can it be changed?

Windows mode and mixed mode (SQL & Windows).
To change authentication mode in SQL Server click Start, Programs, Microsoft SQL Server and click SQL
Enterprise Manager to run SQL Enterprise Manager from the Microsoft SQL Server program group.
Select the server then from the Tools menu select SQL Server Configuration Properties, and choose the
Security page.

Where are SQL server users names and passwords are stored in sql server?

They get stored in master db in the sysxlogins table.
Which command using Query Analyzer will give you the version of SQL server and operating
system?
SELECT SERVERPROPERTY('productversion'), SERVERPROPERTY ('productlevel'), SERVERPROPERTY
('edition')

What is SQL server agent?

SQL Server agent plays an important role in the day-to-day tasks of a database administrator (DBA). It
is often overlooked as one of the main tools for SQL Server management. Its purpose is to ease the
implementation of tasks for the DBA, with its full-function scheduling engine, which allows you to
schedule your own jobs and scripts.

Can a stored procedure call itself or recursive stored procedure? How many level SP nesting
possible?

Yes. Because Transact-SQL supports recursion, you can write stored procedures that call themselves.
Recursion can be defined as a method of problem solving wherein the solution is arrived at by
repetitively applying it to subsets of the problem. A common application of recursive logic is to perform
numeric computations that lend themselves to repetitive evaluation by the same processing steps.
Stored procedures are nested when one stored procedure calls another or executes managed code by
referencing a CLR routine, type, or aggregate. You can nest stored procedures and managed code
references up to 32 levels.

What is @@ERROR?

The @@ERROR automatic variable returns the error code of the last Transact-SQL statement. If there
was no error, @@ERROR returns zero. Because @@ERROR is reset after each Transact-SQL statement,
it must be saved to a variable if it is needed to process it further after checking it.

What is Raiseerror?

Stored procedures report errors to client applications via the RAISERROR command. RAISERROR
doesn't change the flow of a procedure; it merely displays an error message, sets the @@ERROR
automatic variable, and optionally writes the message to the SQL Server error log and the NT
application event log.

What is log shipping?

Log shipping is the process of automating the backup of database and transaction log files on a
production SQL server, and then restoring them onto a standby server. Enterprise Editions only
supports log shipping. In log shipping the transactional log file from one server is automatically updated
into the backup database on the other server. If one server fails, the other server will have the same db
can be used this as the Disaster Recovery plan. The key feature of log shipping is that is will
automatically backup transaction logs throughout the day and automatically restore them on the
standby server at defined interval.

What is the difference between a local and a global variable?

A local temporary table exists only for the duration of a connection or, if defined inside a compound
statement, for the duration of the compound statement.
A global temporary table remains in the database permanently, but the rows exist only within a given
connection. When connection are closed, the data in the global temporary table disappears. However,
the table definition remains with the database for access when database is opened next time.

What command do we use to rename a db?

sp_renamedb ‘oldname’ , ‘newname’
If someone is using db it will not accept sp_renmaedb. In that case first bring db to single user using
sp_dboptions. Use sp_renamedb to rename database. Use sp_dboptions to bring database to multi user
mode.

What is sp_configure commands and set commands?

Use sp_configure to display or change server-level settings. To change database-level settings, use
ALTER DATABASE. To change settings that affect only the current user session, use the SET statement.

What are the different types of replication? Explain.

The SQL Server 2000-supported replication types are as follows:
Transactional
Snapshot
Merge
Snapshot replication distributes data exactly as it appears at a specific moment in time and does not
monitor for updates to the data. Snapshot replication is best used as a method for replicating data that
changes infrequently or where the most up-to-date values (low latency) are not a requirement. When
synchronization occurs, the entire snapshot is generated and sent to Subscribers.
Transactional replication, an initial snapshot of data is applied at Subscribers, and then when data
modifications are made at the Publisher, the individual transactions are captured and propagated to
Subscribers.
Merge replication is the process of distributing data from Publisher to Subscribers, allowing the
Publisher and Subscribers to make updates while connected or disconnected, and then merging the
updates between sites when they are connected.

What are the OS services that the SQL Server installation adds?

MS SQL SERVER SERVICE, SQL AGENT SERVICE, DTC (Distribution transac co-ordinator)
What are three SQL keywords used to change or set someone’s permissions?
GRANT, DENY, and REVOKE.

What does it mean to have quoted_identifier on? What are the implications of having it off?

When SET QUOTED_IDENTIFIER is ON, identifiers can be delimited by double quotation marks, and
literals must be delimited by single quotation marks. When SET QUOTED_IDENTIFIER is OFF, identifiers
cannot be quoted and must follow all Transact-SQL rules for identifiers.

What is the STUFF function and how does it differ from the REPLACE function?

STUFF function to overwrite existing characters. Using this syntax, STUFF(string_expression, start,
length, replacement_characters), string_expression is the string that will have characters substituted,
start is the starting position, length is the number of characters in the string that are substituted, and
replacement_characters are the new characters interjected into the string.
REPLACE function to replace existing characters of all occurance. Using this syntax
REPLACE(string_expression, search_string, replacement_string), where every incidence of
search_string found in the string_expression will be replaced with replacement_string.

Using query analyzer, name 3 ways to get an accurate count of the number of records in a
table?

SELECT * FROM table1
SELECT COUNT(*) FROM table1
SELECT rows FROM sysindexes WHERE id = OBJECT_ID(table1) AND indid < 2

How to rebuild Master Database?

Shutdown Microsoft SQL Server 2000, and then run Rebuildm.exe. This is located in the Program
Files\Microsoft SQL Server\80\Tools\Binn directory.
In the Rebuild Master dialog box, click Browse.
In the Browse for Folder dialog box, select the \Data folder on the SQL Server 2000 compact disc or in
the shared network directory from which SQL Server 2000 was installed, and then click OK.
Click Settings. In the Collation Settings dialog box, verify or change settings used for the master
database and all other databases.
Initially, the default collation settings are shown, but these may not match the collation selected during
setup. You can select the same settings used during setup or select new collation settings. When done,
click OK.
In the Rebuild Master dialog box, click Rebuild to start the process.
The Rebuild Master utility reinstalls the master database.
To continue, you may need to stop a server that is running.


What is the basic functions for master, msdb, model, tempdb databases?

The Master database holds information for all databases located on the SQL Server instance and is the
glue that holds the engine together. Because SQL Server cannot start without a functioning master
database, you must administer this database with care.
The msdb database stores information regarding database backups, SQL Agent information, DTS
packages, SQL Server jobs, and some replication information such as for log shipping.
The tempdb holds temporary objects such as global and local temporary tables and stored procedures.
The model is essentially a template database used in the creation of any new user database created in
the instance.

What are primary keys and foreign keys?

Primary keys are the unique identifiers for each row. They must contain unique values and cannot be
null. Due to their importance in relational databases, Primary keys are the most fundamental of all keys
and constraints. A table can have only one Primary key.
Foreign keys are both a method of ensuring data integrity and a manifestation of the relationship
between tables.

What is data integrity? Explain constraints?

Data integrity is an important feature in SQL Server. When used properly, it ensures that data is
accurate, correct, and valid. It also acts as a trap for otherwise undetectable bugs within applications.
A PRIMARY KEY constraint is a unique identifier for a row within a database table. Every table should
have a primary key constraint to uniquely identify each row and only one primary key constraint can be
created for each table. The primary key constraints are used to enforce entity integrity.
A UNIQUE constraint enforces the uniqueness of the values in a set of columns, so no duplicate values
are entered. The unique key constraints are used to enforce entity integrity as the primary key
constraints.
A FOREIGN KEY constraint prevents any actions that would destroy links between tables with the
corresponding data values. A foreign key in one table points to a primary key in another table. Foreign
keys prevent actions that would leave rows with foreign key values when there are no primary keys
with that value. The foreign key constraints are used to enforce referential integrity.
A CHECK constraint is used to limit the values that can be placed in a column. The check constraints
are used to enforce domain integrity.
A NOT NULL constraint enforces that the column will not accept null values. The not null constraints
are used to enforce domain integrity, as the check constraints.

What are the properties of the Relational tables?

Relational tables have six properties:

Values are atomic.
Column values are of the same kind.
Each row is unique.
The sequence of columns is insignificant.
The sequence of rows is insignificant.
Each column must have a unique name.

What is De-normalization?

De-normalization is the process of attempting to optimize the performance of a database by adding
redundant data. It is sometimes necessary because current DBMSs implement the relational model
poorly. A true relational DBMS would allow for a fully normalized database at the logical level, while
providing physical storage of data that is tuned for high performance. De-normalization is a technique
to move from higher to lower normal forms of database modeling in order to speed up database access.

How to get @@error and @@rowcount at the same time?

If @@Rowcount is checked after Error checking statement then it will have 0 as the value of
@@Recordcount as it would have been reset.
And if @@Recordcount is checked before the error-checking statement then @@Error would get reset.
To get @@error and @@rowcount at the same time do both in same statement and store them in local
variable. SELECT @RC = @@ROWCOUNT, @ER = @@ERROR

What is Identity?

Identity (or AutoNumber) is a column that automatically generates numeric values. A start and
increment value can be set, but most DBA leave these at 1. A GUID column also generates numbers,
the value of this cannot be controled. Identity/GUID columns do not need to be indexed.

What is a Scheduled Jobs or What is a Scheduled Tasks?

Scheduled tasks let user automate processes that run on regular or predictable cycles. User can
schedule administrative tasks, such as cube processing, to run during times of slow business activity.
User can also determine the order in which tasks run by creating job steps within a SQL Server Agent
job. E.g. Back up database, Update Stats of Tables. Job steps give user control over flow of execution.
If one job fails, user can configure SQL Server Agent to continue to run the remaining tasks or to stop
execution.

What is a table called, if it does not have neither Cluster nor Non-cluster Index? What is it
used for?

Unindexed table or Heap. Microsoft Press Books and Book On Line (BOL) refers it as Heap.
A heap is a table that does not have a clustered index and, therefore, the pages are not linked by
pointers. The IAM pages are the only structures that link the pages in a table together.
Unindexed tables are good for fast storing of data. Many times it is better to drop all indexes from table
and than do bulk of inserts and to restore those indexes after that.

What is BCP? When does it used?

BulkCopy is a tool used to copy huge amount of data from tables and views. BCP does not copy the
structures same as source to destination.
How do you load large data to the SQL server database?
BulkCopy is a tool used to copy huge amount of data from tables. BULK INSERT command helps to
Imports a data file into a database table or view in a user-specified format.

Can we rewrite subqueries into simple select statements or with joins?

Subqueries can often be re-written to use a standard outer join, resulting in faster performance. As we
may know, an outer join uses the plus sign (+) operator to tell the database to return all non-matching
rows with NULL values. Hence we combine the outer join with a NULL test in the WHERE clause to
reproduce the result set without using a sub-query.

Can SQL Servers linked to other servers like Oracle?

SQL Server can be lined to any server provided it has OLE-DB provider from Microsoft to allow a link.
E.g. Oracle has a OLE-DB provider for oracle that Microsoft provides to add it as linked server to SQL
Server group.

How to know which index a table is using?

SELECT table_name,index_name FROM user_constraints
How to copy the tables, schema and views from one SQL server to another?
Microsoft SQL Server 2000 Data Transformation Services (DTS) is a set of graphical tools and
programmable objects that lets user extract, transform, and consolidate data from disparate sources
into single or multiple destinations.

What is Self Join?

This is a particular case when one table joins to itself, with one or two aliases to avoid confusion. A self
join can be of any type, as long as the joined tables are the same. A self join is rather unique in that it
involves a relationship with only one table. The common example is when company have a hierarchal
reporting structure whereby one member of staff reports to another.

What is Cross Join?

A cross join that does not have a WHERE clause produces the Cartesian product of the tables involved
in the join. The size of a Cartesian product result set is the number of rows in the first table multiplied
by the number of rows in the second table. The common example is when company wants to combine
each product with a pricing table to analyze each product at each price.
Which virtual table does a trigger use?

Inserted and Deleted.

List few advantages of Stored Procedure

Stored procedure can reduced network traffic and latency, boosting application performance.
Stored procedure execution plans can be reused, staying cached in SQL Server's memory,
Stored procedures help promote code reuse. Stored procedures can encapsulate logic. You can change stored procedure code without affecting clients.Stored procedures provide better security to your data.

What is DataWarehousing?

Subject-oriented, meaning that the data in the database is organized so that all the data
elements relating to the same real-world event or object are linked together;
Time-variant, meaning that the changes to the data in the database are tracked and recorded
so that reports can be produced showing changes over time;
Non-volatile, meaning that data in the database is never over-written or deleted, once
committed, the data is static, read-only, but retained for future reporting;
Integrated, meaning that the database contains data from most or all of an organization's
operational applications, and that this data is made consistent.

What is OLTP(OnLine Transaction Processing)?

In OLTP - online transaction processing systems relational database design use the discipline of data
modeling and generally follow the Codd rules of data normalization in order to ensure absolute data
integrity. Using these rules complex information is broken down into its most simple structures (a table)
where all of the individual atomic level elements relate to each other and satisfy the normalization

How do SQL server 2000 and XML linked? Can XML be used to access data?

FOR XML (ROW, AUTO, EXPLICIT)
You can execute SQL queries against existing relational databases to return results as XML rather than
standard rowsets. These queries can be executed directly or from within stored procedures. To retrieve
XML results, use the FOR XML clause of the SELECT statement and specify an XML mode of RAW, AUTO,
or EXPLICIT.
OPENXML
OPENXML is a Transact-SQL keyword that provides a relational/rowset view over an in-memory XML
document. OPENXML is a rowset provider similar to a table or a view. OPENXML provides a way to
access XML data within the Transact-SQL context by transferring data from an XML document into the
relational tables. Thus, OPENXML allows you to manage an XML document and its interaction with the
relational environment.

What is an execution plan? When would you use it? How would you view the execution plan?

An execution plan is basically a road map that graphically or textually shows the data retrieval methods
chosen by the SQL Server query optimizer for a stored procedure or ad-hoc query and is a very useful
tool for a developer to understand the performance characteristics of a query or stored procedure since
the plan is the one that SQL Server will place in its cache and use to execute the stored procedure or
query. From within Query Analyzer is an option called "Show Execution Plan" (located on the Query
drop-down menu). If this option is turned on it will display query execution plan in separate window
when query is ran again.

Pagination on the Sql

To get the data form the data base based on UI pagination we can use the following Query.This query make use of the With Statement for achiving this task

DECLARE @StartRow INT,@PageSize INT,@PageIndex INT
SELECT @PageIndex = 5, @PageSize = 5
-- Retriving Paged Data
DECLARE @FirstRow INT,@LastRow INT
set @StartRow=@PageIndex*@PageSize

SELECT @FirstRow = @StartRow + 1, @LastRow = @PageSize + @StartRow;
WITH Members AS
(

      SELECT Coloumn1, Coloumn2, Coloumn3, Coloumn4, Coloumn5
      ROW_NUMBER() OVER (ORDER BY Coloumn1 ASC) AS RowNumber

      FROM TableName1
)
SELECT RowNumber,Coloumn1, Coloumn2, Coloumn3, Coloumn4, Coloumn5 FROM
Members
WHERE RowNumber BETWEEN @FirstRow AND @LastRow OR @PageSize = -1
ORDER BY RowNumber ASC;

Creating Folder and writtings file in JavaScript on the Client Via Active X

This function will create a folder and and Create a file inside that folder and writes the data into the file using the activex object .Inorder to do this we should enable the option on the browser -Enable active x object that marked as unsafe form the option menu of the IE

       function Callme() {
           var Tristate = 0;
           var Writing = 2;
           var myActiveXObject = new ActiveXObject("Scripting.FileSystemObject");
           myActiveXObject.CreateFolder("C:\\Myfolder");
           file = myActiveXObject.CreateTextFile("c:\\Myfolder\\erroLog.xml");
           var stringText = "";
           stringText = "";
           stringText += "\nTove";
           stringText += "\nJani";
           stringText += "\nReminder";
           stringText += "\nDon't forget me this weekend!";
           stringText += "\n";
           file.Write(stringText);
           file = myActiveXObject.CreateTextFile("c:\\Myfolder\\erroLog.txt");
           stringText = "This is a test";
           file.Write(stringText);
           return false;
       }

Sql Query for specific column for the Database

Here is a SQL query, where we get the  list of table names  which contain a specific column.

Ex: Column name = internalOrderNumber.

If I want to know in how many tables this column name is present, here is a query which gives the result !!

SELECT name FROM sysobjects WHERE id IN ( SELECT id FROM syscolumns WHERE name like '%InternalOrderNumber%' ) and xtype='U'

Remove View State for the Asp.net Page

                        This Code Sippnet give you a clean solution on the removal of the view state for  the page and Stored it across in any storage area .By doing like this you can achieve a greater performance on the renderning part  and on the page size.All that we required is to override the LoadPageStateFromPersistenceMedium method on the page .If this is done at the base level of your application then all that we required to inherit from there

protected override object LoadPageStateFromPersistenceMedium()
    {
        try
        {
            return LoadViewState();

        }
        catch
        {
            return base.LoadPageStateFromPersistenceMedium();
        }
    }

The following Sippnet does a saving the view state .Normally it saves to a hidden field inside the page  and once the page is requested it takes from the hidden field and creates the contols and set the state .if we customise here then the state will be saved where ever you want and get the from there on the obove function

    protected override void SavePageStateToPersistenceMedium(object
viewState)
    {
        try
        {
           SaveViewState(viewState);

        }
        catch
        {
            base.SavePageStateToPersistenceMedium(viewState);
        }

    }


    private object LoadViewState()
    {
        if (_formatter == null)
        {
            _formatter = new LosFormatter();
        }
        if (null == Request.Form[VIEW_STATE_FIELD_NAME])
        {
            return null;
        }
        string _viewState =HttpContext.Current.Cache[Request.Form[VIEW_STATE_FIELD_NAME].ToString()].ToString();
        if (_viewState == null)
            return null;
        else
            return _formatter.Deserialize(_viewState);
    }

    private void SaveViewState(object viewState)
    {
        string str = "VIEWSTATE_" + Request.UserHostAddress + "_"
            +Session.SessionID+"_"+ DateTime.Now.Ticks.ToString();
        if (_formatter == null)
        {
            _formatter = new LosFormatter();
        }
        StringBuilder _viewState = new StringBuilder();
        StringWriter _writer = new StringWriter(_viewState);
        _formatter.Serialize(_writer, viewState);
        HttpContext.Current.Cache.Add(str, _viewState.ToString(),null,      
       DateTime.Now.AddMinutes(Session.Timeout), TimeSpan.Zero,
        CacheItemPriority.Default, null);
        RegisterHiddenField(VIEW_STATE_FIELD_NAME, str);
    } 

For serlization for the viewstate we have to use  LOS(Limited Object Serlization ).............