What is NOLOCK ?

Using the NOLOCK query optimizer 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 meansthat another process could be updating the data at the exact time you are reading it. Therare 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) lockThis 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 readshave completed, and reads requested after the update will wait for the updates to complete. The result to your system is delay (blocking)

What is use of EXCEPT clause?

EXCEPT clause is similar to MINUreturns all rows in the first query that are not returned in the second query. Each SQL statement within the EXCEPT query and MINUS query must have the same number of fieldsin the result sets with similar ata types. (

What is Isolation Levels?

Transactions specify an isolation level that defines the degree to which one transaction must be isolated from resource or datamodifications made by other transactions. Isolation levels are described in terms of which concurrency side‐effects, such as dirty reads or phantom reads, are allowed.

What is LINQ?

Language Integrated Query (LINQ) adds the ability to query objects using .NET languages. The LINQ to SQL object/relational mapping (O/RM) framework provides the following basic features:

• Tools to create classes (usually called entities) mapped to database tables
• Compatibility with LINQ’s standard query operations
• The DataContext class, with features such as entity record monitoring, automatic SQL statement generation, record concurrency detection, and much more

What are synonyms?

Synonyms give you the ability to provide alternate names for database objects. You can alias object names; for example, using the Employee table as Emp. You can also shorten names. This is especially useful when dealing with three and four part names; for example, shortening server.database.owner.object to object.

What is CLR?

In SQL Server 2008, SQL Server objects such as user‐defined functions can be created using such CLR languages. This CLR language support extends not only to user‐defined functions, but also to stored procedures and triggers. You can develop such CLR add‐ons to SQL Server using Visual Studio 2008.

How can we rewrite sub‐queries into simple select statements or with joins?

Yes we can write using Common Table Expression (CTE). A Common Table Expression (CTE) is an expression that can be thought of as a temporary result set which is defined within the execution of a single SQL statemnt. A CTE is similar to a derived table in that it is not stored as an object and lasts only for the duration of the query.

E.g.
USE AdventureWorks
GO WITH EmployeeDepartment_CTE AS
( SELECT EmployeeID,DepartmentID,ShiftID FROM HumanResources.EmployeeDepartmentHistory )
SELECT ecte.EmployeeId,ed.DepartmentID, ed.Name,ecte.ShiftID
FROM HumanResources.Department ed
INNER JOIN EmployeeDepartment_CTE ecte ON ecte.DepartmentID = ed.DepartmentID
GO

What are the Advantages of using CTE?

• Using CTE improves the readability and makes maintenance of complex queries easy.
• The query can be divided into separate, simple, logical building blocks which can be then used to build more complex CTEs until final result set is generated.
• CTE can be defined in functions, stored procedures, triggers or even views.
  
• After a CTE is defined, it can be used as a Table or a View and can SELECT, INSERT, UPDATE or DELETE Data.

Which are new data types introduced in SQL SERVER 2008?

The GEOMETRY Type: The GEOMETRY data type is a system .NET common language runtime (CLR) data type in SQL Server. This type represents data in a two‐dimensional Euclidean coordinate system.

The GEOGRAPHY Type: The GEOGRAPHY datatype’s functions are the same as with GEOMETRY. The difference between the two is that when you specify GEOGRAPHY, you are usually specifying points in terms of latitude and longitude.

New Date and Time Datatypes: SQL Server 2008 introduces four new datatypes related to date and time: DATE, TIME, DATETIMEOFFSET, and DATETIME2. •

• DATE: The new DATE type just stores the date itself. It is based on the Gregorian calendar and handles years from 1 to 9999.
• TIME: The new TIME (n) type stores time with a range of 00:00:00.0000000 through 23:59:59.9999999. The precision is allowed with this type. TIME supports seconds down to 100 nanoseconds. The n in TIME (n) defines this level of fractional second precision, from 0 to 7 digits of precision.
• The DATETIMEOFFSET Type: DATETIMEOFFSET (n) is the time‐zone‐aware version of a datetime datatype. The name will appear less odd when you consider what it really is: a date + a time + a time‐zone offset. The offset is based on how far behind or ahead you are from Coordinated Universal Time (UTC) time.
• The DATETIME2 Type: It is an extension of the datetime type in earlier versions of SQL Server. This new datatype has a date range covering dates from January 1 of year 1 through December 31 of year 9999. This is a definite improvement over the 1753 lower boundary of the datetime datatype. DATETIME2 not only includes the larger date range, but also has a timestamp and the same fractional precision that TIME type provides

What is Filtered Index?

Filtered Index is used to index a portion of rows in a table that means it applies filter on INDEX which improves query performnce, reduce index maintenance costs, and reduce index storage costs compared with full‐table indexes. When we see an Index created with some where clause then that is actually a FILTERED INDEX.  

What is MERGE Statement?

MERGE is a new feature that provides an efficient way to perform multiple DML operations. In previous versions of SQL Server, we had to write separate statements to INSERT, UPDATE, or DELETE data based on certain conditions, but now, using MERGE statement we can include the logic of such data modifications in one statement that even checks when the data is mtched then just update it and when unmatched then insert it. One of the most important advantages of MERGE statement is all the data is read and processed only once.  

What is CTE?

 CTE is an abbreviation Common Table Expression. A Common Table Expression (CTE) is an expression that can be thought of as a temporary result set which is defined within the execution of a single SQL statemnt. A CTE is similar to a derived table in that it is not stored as an object and lasts only for the duration of the query.

What does TOP Operator Do?

 The TOP operator is used to specify the number of rows to be returned by a query. The TOP operator has new addition in SQL SERVER 2008 that it accepts variables as well as literal values and can be used with NSERT, UPDATE, and DELETES statements. 

What are Sparse Columns?

 A sparse column is another tool used to reduce the amount of physical storage used in a database. They are the ordinary columns that have an optimized storage for null values. Sparse columns reduce the space requirements for null values at the cost of more overhead to retrieve nonnull values.

What is Replication and Database Mirroring?

Database mirroring can be used with replication to provide availability for the publication database. Database mirroring involves two copies of a single database that typically reside on different computers. At any given time, only one copy of the database is currently available to clients which are known as the principal database. Updates made by clients to the principal database are applied on the other copy of the database, known as the mirror database. Mirroring involves applying the transaction log from every insertion, update, or deletion made on the principal database onto the mirror database.

What is Policy Management?

Policy Management in SQL SERVER 2008 allows you to define and enforce policies for configuring and managing SQL Server across te enterprise. Policy‐Based Management is configured in SQL Server Management Studio (SSMS). Navigate to the Object Explorer and expand the Management node and the Policy Management node; you will see the Policies, Conditions, and Facets nodes.

What is Service Broker?

Service Broker is a message‐queuing technology in SQL Server that allows developers to integrate SQL Server fully into distributed applications.
Service Broker is feature which provides facility to SQL Server to send an asynchronous, transactional message.
it allows a database to send a message to another database without waiting for the response, so the application will continue to function if the remote database is temporarily unavailable.

What are the basic functions for master, msdb, model, tempdb and resource databases? (sql server 2008)

The master database holds information for all databases located on the SQL Server instance and is theglue that holds the engine together. Because SQL Server cannot start without a functioning masterdatabase, 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.

The resoure Database is a read‐only database that contains all the system objects that are included with SQL Server. SQL Server system objects, such as sys.objects, are physically persisted in the Resource database, but they logically appear in the sys schema of every database. The Resource database does not contain user data or user metadata.

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 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 controlled. Identity/GUID columns do not need to be indexed.