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What is a constraint in SQL Server?

Posted By :volvo     Posted Date :December 25, 2013    Points :40   Category :Sql Server 
Constraint in SQL Server can be used to specify the limit on the data type of table. It can be specified while creating or altering the table statement. following constraints are SQL Server Query.
NOT NULL.
CHECK.
DEFAULT.
UNIQUE.
PRIMARY KEY.
FOREIGN KEY.

You can also find related Interview Question to What is a constraint in SQL Server?  below: 

Database Concurrency in Sql Server.

  
When two or more user try to update same type of data in a table then Database Concurrency helps in this situation.

There are 2 types of Database Concurrency

Pessimistic: When one user try to change the data with pessimistic concurrency then a lock is placed on the data in a table so that another user cannot change data. when one user finishes then other user can able to change.

Optimistic: When two user works on the same data in a table and one change that data first then second user cannot change that same data becasue the which he have using is allready changed so he cannot do the change becasue change apply to another data that is changed by first user. (More...)

Is it true that COM objects no longer need to be registered on the server?

  
Yes and No. Legacy COM objects still need to be registered on the server before they can be used. COM developed using the new .NET Framework will not need to be registered. Developers will be able to auto-register these objects just by placing them in the 'bin' folder of the application. (More...)

What are server controls?

  
ASP.NET server controls are components that run on the server and encapsulate user-interface and other related functionality. They are used in ASP.NET pages and in ASP.NET code-behind classes. (More...)

Which authentication mode lets you use both SQL Server logins and Windows logins?

  
Mixed Mode authentication mode lets you use both SQL Server logins and Windows logins? (More...)

What are the types of indexes available with SQL Server?

  
There are basically two types of indexes that we use with the SQL Server. Clustered and the Non-Clustered. (More...)

What is the difference between Server. Transfer and Response. Redirect?

  
The Transfer method allows you to transfer from inside one ASP page to another ASP page. All of the state information that has been created for the first (calling) ASP page will be transferred to the second (called) ASP page. This transferred information includes all objects and variables that have been given a value in an Application or Session scope, and all items in the Request collections. For example, the second ASP page will have the same SessionID as the first ASP page.

When the second (called) ASP page completes its tasks, you do not return to the first (calling) ASP page. All these happen on the server side browser is not aware of this.
The redirect message issue HTTP 304 to the browser and causes browser to got the specified page. Hence there is round trip between client and server. Unlike transfer, redirect doesn't pass context information to the called page.


Shashi Ray (More...)

How many types of tables are present in SQL SERVER?

  
There are 2 types of temporary tables, local and global in sql server.

Local temporary tables are created using a single pound (#) sign and are visible to a single connection and automatically dropped when that connection ends.

Global temporary tables are created using a double pound (##) sign and are visible across multiple connections and users and are automatically dropped when all SQL sessions stop referencing the global temporary table. (More...)

Difference between Server.Transfer & Response.Redierect ?

  
Server.Transfer-

1)Server.Transfer transfers page processing from one page directly to the next page without making a round-trip back to the client's browser. This provides a faster response with a little less overhead on the server.

2) Server.Transfer does not update the clients url history list or current url.

Response.Redirect-

1)Response.Redirect is used to redirect the user's browser to another page or site. This performas a trip back to the client where the client's browser is redirected to the new page.

2) The user's browser history list is updated to reflect the new address. (More...)

What is SQL Server Service broker?

  
Service Broker is a unique feature in Microsoft SQL Server 2005 which is used to by internal or external processes to send and receive guaranteed, asynchronous messages by using extensions to Transact-SQL Data Manipulation Language (DML).

It's a platform for building a new class of loosely coupled services for database applications. Service Broker not only brings asynchronous, queued messaging to database applications but significantly expands the state of the art for reliable messaging.

The key components of SQL Server Service broker are
.Queue stores the messages for a particular service.
.Dialog is a conversation between two services.
.Conversation group is a group of related conversations. Every conversation belongs to exactly one conversation group.
.Activation specifies a stored procedure that will handle messages destined for a particular service. (More...)

What are the essential components of SQL Server Service broker?

  
Queues
Service Broker uses queues to provide loose coupling between the message sender and the message receiver. The sender can put a message in a queue and then continue on with the application, relying on Service Broker to ensure that the message reaches its destination. Queues permit a lot of scheduling flexibility.

Dialogs
Dialogs are bidirectional streams of messages between two endpoints. All messages in a dialog are ordered, and dialog messages are always delivered in the order they are sent. The order is maintained across transactions, across input threads, across output threads, and across crashes and restarts.

Conversation Groups
It's a way of grouping all the dialogs that are used for a particular task. All the dialogs associated with processing a particular order would be grouped into a single conversation group. The conversation group is implemented as a conversation group identifier, which is included with all messages in all dialogs contained in the conversation group. When a message is received from any of the dialogs in a conversation group, the conversation group is locked with a lock that is held by the receiving transaction. For the duration of the transaction, only the thread that holds the lock can receive messages from any of the dialogs in the conversation group. This makes our order entry application much easier to write because even though we use many threads for scalability, any particular order is only processed on one thread at a time. This means we don't have to make our application resilient to problems that are caused by the simultaneous processing of a single order on multiple threads.

Activation
You use the activation feature of Service Broker to specify a stored procedure that will handle messages destined for a particular service. When messages arrive for a service, Service Broker checks whether there is a stored procedure running that can process the messages. If there isn't a running message-processing stored procedure, Service Broker starts one. The stored procedure then processes messages until the queue is empty, after which it terminates. Moreover, if Service Broker determines that messages are arriving faster than the stored procedure can process them, it starts additional instances of the stored procedure until enough are running to keep up with the incoming messages (or until the configured maximum number is reached). This ensures that the right number of resources for processing incoming messages are always available. (More...)

Explain Constraints in SQL SERVER?

  
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:

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.

UNIQUE constraint:

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.

FOREIGN KEY constraint:

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.

CHECK constraint:

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. (More...)

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