Sqlserver Interview questions

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. (Read More Here)

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 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 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. (Read More Here)

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 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.
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.