Question: What is RDBMS?
Answer: 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.
Question: What is normalization?
Answer:
Database normalization is a data design and organization process applied to
data structures based on rules that help build relational databases. In
relational database design, the process of organizing data to minimize
redundancy. 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.
Question: What are different normalization forms?
Answer: 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
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.
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.
Question: What is Stored Procedure?
Answer: 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.
Question: What is Trigger?
Answer: 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; the 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.
Question: What is View?
Answer: 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.
Question: What is Index?
Answer: 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.
Clustered indexes define the physical sorting of a database table’s rows in
the storage media. For this reason, each database table may have only one
clustered index.
Non-clustered indexes are created outside of the database table and contain a
sorted list of references to the table itself.
