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. Stored Procedure sp_addlinkedserver, sp_addlinkedsrvlogin will be used add new Linked Server.

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 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; 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 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 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.

What are different transaction levels in SQL SERVER?

There are four transaction levels in SQL SERVER :-

READ COMMITTED
The shared lock is held for the duration of the transaction, meaning that no other
transactions can change the data at the same time. Other transactions can insert and
modify data in the same table, however, as long as it is not locked by the first transaction.

READ UNCOMMITTED
No shared locks and no exclusive locks are honored. This is the least restrictive isolation level resulting in the best concurrency but the least data integrity.

REPEATABLE READ
This setting disallows dirty and non-repeatable reads. However, even though the locks
are held on read data, new rows can still be inserted in the table, and will subsequently be interpreted by the transaction.

SERIALIZABLE
This is the most restrictive setting holding shared locks on the range of data. This setting does not allow the insertion of new rows in the range that is locked; therefore, no phantomsare allowed.

Following is the syntax for setting transaction level in SQL SERVER.
SET TRANSACTION ISOLATION LEVEL SERIALIZABLE

What is the difference between DELETE TABLE and TRUNCATE TABLE commands?

Following are difference between them :-

√ DELETE TABLE syntax logs the deletes thus make the delete operation
slow. TRUNCATE table does not log any information but it logs information
about deallocation of data page of the table so TRUNCATE table is faster as
compared to delete table.

√ DELETE table can have criteria while TRUNCATE can not.

√ TRUNCATE table can not trigger.

What are indexes?

Indexes in SQL Server are similar to the indexes in books. They help SQL Server retrieve the data quickly.

There are clustered and nonclustered indexes.
A clustered index is a special type of index that reorders the way in which records in the table are physically stored. Therefore tablecan 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 is a candidate key ?

A table may have more than one combination of columns that could uniquely identify the
rows in a table; each combination is a candidate key. During database design you can pick up one of the candidate keys to be the primary key. For example, in the supplier table supplierid and suppliername can be candidate key but you will only pick up supplierid as the primary key.

What is denormalization ?

Denormalization is the process of putting one fact in numerous places (its vice-versa of normalization).Only one valid reason exists for denormalizing a relational design - to enhance performance.The sacrifice to performance is that you increase redundancy in
database.

What is denormalization ?

Denormalization is the process of putting one fact in numerous places (its vice-versa of normalization).Only one valid reason exists for denormalizing a relational design - to enhance performance.The sacrifice to performance is that you increase redundancy in
database.

What is normalization? What are different types of normalization?

It is set of rules that have been established to aid in the design of tables that are meant to be connected through relationships. This set of rules is known as Normalization.

Benefits of normalizing your database will include:
√ Avoiding repetitive entries
√ Reducing required storage space
√ Preventing the need to restructure existing tables to accommodate new data.
√ Increased speed and flexibility of queries, sorts, and summaries.

Following are the three normal forms :-

First Normal Form
For a table to be in first normal form, data must be broken up into the smallest units possible.In addition to breaking data up into the smallest meaningful values, tables in first normal form should not contain repetitions groups of fields.

Second Normal form
The second normal form states that each field in a multiple field primary keytable must be directly related to the entire primary key. Or in other words, each non-key field should be a fact about all the fields in the primary key.

Third normal form
A non-key field should not depend on other Non-key field.