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What is the difference between Select() and SelectMany()?
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Posted Date :
May 12, 2011
Select() converts one type to another and returns enumerable.
SelectMany() flattens the elements and gives a combined list of elements.
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What is the difference between Select() and SelectMany()?
Difference between Set and Select keyword in sql server?
1.Set is a ANSI standard for variable assignment.
2.We can assign only one variable at a time
3.When assigning from a query that returns more than one value, SET will fail with an error.
1.Select is a Non-ANSI standard when assigning variables.
2.We can assign multiple variable at a time
3.When assigning from a query that returns more than one value, SELECT will assign the last value returned by the query and hide the fact that the query returned
Difference between Set and Select ?
Set is a ANSI standard for variable assignment.
We can assign only one variable at a time
Select is a Non-ANSI standard when assigning variables.
We can assign multiple variable at a time
What is the difference between SET and SELECT?
Both SET and SELECT can be used to assign values to variables. It is recommended that SET @local_variable be used for variable assignment rather than SELECT @local_variable.
declare @i int
This is used to assign constant values.
select @i=max(column_name)from table_name
select @i=max(emp_id) from table_emp.
Difference Between Delete and Truncate
.Delete table is a logged operation, so the deletion of each row gets logged in the transaction log, which makes it slow.
. Truncate table also deletes all the rows in a table, but it won't log the deletion of each row, instead it logs the de-allocation of the data pages of the table, which makes it faster. Of course, truncate table cannot be rolled back.
. Truncate table is functionally identical to delete statement with no "where clause" both remove all rows in the table. But truncate table is faster and uses fewer system and transaction log resources than delete.
. Truncate table removes all rows from a table, but the table structure and its columns, constraints, indexes etc., remains as it is.
. In truncate table the counter used by an identity column for new rows is reset to the seed for the column.
. If you want to retain the identity counter, use delete statement instead.
. If you want to remove table definition and its data, use the drop table statement.
. You cannot use truncate table on a table referenced by a foreign key constraint; instead, use delete statement without a where clause. Because truncate table is not logged, it cannot activate a trigger.
. Truncate table may not be used on tables participating in an indexed view.
Difference between assembly manifest & metadata?
assembly manifest - An integral part of every assembly that renders the assembly self-describing. The assembly manifest contains the assembly's metadata. The manifest establishes the assembly identity, specifies the files that make up the assembly implementation, specifies the types and resources that make up the assembly, itemizes the compile-time dependencies on other assemblies, and specifies the set of permissions required for the assembly to run properly. This information is used at run time to resolve references, enforce version binding policy, and validate the integrity of loaded assemblies. The self-describing nature of assemblies also helps makes zero-impact install and XCOPY deployment feasible.
metadata - Information that describes every element managed by the common language runtime: an assembly, loadable file, type, method, and so on. This can include information required for debugging and garbage collection, as well as security attributes, marshaling data, extended class and member definitions, version binding, and other information required by the runtime.
What is the difference between ref & out parameters?
An argument passed to a ref parameter must first be initialized. Compare this to an out parameter, whose argument does not have to be explicitly initialized before being passed to an out parameter.
What is the difference between a Struct and a Class?
The struct type is suitable for representing lightweight objects such as Point, Rectangle, and Color. Although it is possible to represent a point as a class, a struct is more efficient in some scenarios. For example, if you declare an array of 1000 Point objects, you will allocate additional memory for referencing each object. In this case, the struct is less expensive.
When you create a struct object using the new operator, it gets created and the appropriate constructor is called. Unlike classes, structs can be instantiated without using the new operator. If you do not use new, the fields will remain unassigned and the object cannot be used until all of the fields are initialized.
It is an error to declare a default (parameterless) constructor for a struct. A default constructor is always provided to initialize the struct members to their default values.
It is an error to initialize an instance field in a struct.
There is no inheritance for structs as there is for classes. A struct cannot inherit from another struct or class, and it cannot be the base of a class. Structs, however, inherit from the base class Object. A struct can implement interfaces, and it does that exactly as classes do.
A struct is a value type, while a class is a reference type.
Difference between type constructor and instance constructor? What is static constructor, when it will be fired? And what is its use?
(Class constructor method is also known as type constructor or type initializer)
Instance constructor is executed when a new instance of type is created and the class constructor is executed after the type is loaded and before any one of the type members is accessed. (It will get executed only 1st time, when we call any static methods/fields in the same class.) Class constructors are used for static field initialization. Only one class constructor per type is permitted, and it cannot use the vararg (variable argument) calling convention.
What is the difference between Finalize and Dispose (Garbage collection)
Class instances often encapsulate control over resources that are not managed by the runtime, such as window handles (HWND), database connections, and so on. Therefore, you should provide both an explicit and an implicit way to free those resources. Provide implicit control by implementing the protected Finalize Method on an object (destructor syntax in C# and the Managed Extensions for C++). The garbage collector calls this method at some point after there are no longer any valid references to the object.
In some cases, you might want to provide programmers using an object with the ability to explicitly release these external resources before the garbage collector frees the object. If an external resource is scarce or expensive, better performance can be achieved if the programmer explicitly releases resources when they are no longer being used. To provide explicit control, implement the Dispose method provided by the IDisposable Interface. The consumer of the object should call this method when it is done using the object. Dispose can be called even if other references to the object are alive.
Note that even when you provide explicit control by way of Dispose, you should provide implicit cleanup using the Finalize method. Finalize provides a backup to prevent resources from permanently leaking if the programmer fails to call Dispose.
Difference between OLEDB Provider and SqlClient ?
SQLClient .NET classes are highly optimized for the .net / sqlserver combination and achieve optimal results. The SqlClient data provider is fast. It's faster than the Oracle provider, and faster than accessing database via the OleDb layer. It's faster because it accesses the native library (which automatically gives you better performance), and it was written with lots of help from the SQL Server team.
What is the difference between interface and abstract class ?
a class may inherit several interfaces, a class may inherit only one abstract class
What is the Difference between #Bind and #Eval ?
Eval is read only. Bind is 2 way binding(updatable)
What is the difference between ViewState and SessionState?
ViewState persist the values of controls of particular page in the client when post back operation done. When user requests another page previous page data no longer available.
SessionState persist the data of particular user in the server. This data available till user close the browser or session time completes.
What is the difference between Codebehind="MyCode.aspx.cs" and Src="MyCode.aspx.cs"?
CodeBehind is relevant to Visual Studio.NET only.
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