General Questions of SQL SERVER
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. (
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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 Normalization?
Database normalization is a data design
and organization process applied to data structures based on rules that
help building relational databases. In relational database design, the
process of organizing data to minimize redundancy is called
normalization. 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. (
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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 is said to be in DKNF.
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 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 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; 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. (
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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.
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. (
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For More:
http://blog.sqlauthority.com/2008/09/12/sql-server-2008-interview-questions-and-answers-part-1/
i/ˈæbdʊl kəˈlɑːm/; 15 October 1931 – 27 July 2015) was the 11th President of India from 2002 to 2007. A career scientist turned politician, Kalam was born and raised in Rameswaram, Tamil Nadu, and studied physics and aerospace engineering. He spent the next four decades as a scientist and science administrator, mainly at the Defence Research and Development Organisation (DRDO) and Indian Space Research Organisation (ISRO) and was intimately involved in India's civilian space program and military missile development efforts.[2] He thus came to be known as the Missile Man of India for his work on the development of ballistic missile and launch vehicle technology.[3][4][5] He also played a pivotal organizational, technical, and political role in India's Pokhran-II nuclear tests in 1998, the first since the original nuclear test by India in 1974.[6]
