If yes the you have landed on the right page. Here we are giving most important SQL server interview questions frequently asked during project viva or interview. So lets go ahead for Important SQL server interview questions.

Q. 1 Define Primary Key?

Ans:  The primary key is the columns used to uniquely identify each row of a table.A table can have only one primary key. A primary key value can not appear in more than one row in the table.

Q.2  Define Unique Key?

Ans:  Unique key is a one or more column that must be unique for each row of the table.It is similar to primary key. Primary key column will not accept a null. Whereas the unique key column will accept a null values.

Q. 3 Define Foreign Key?

Ans:  A foreign Key is a combination of columns with value is based on the primary key values from another table. A foreign key constraint also known as Referential Integrity Constraint.

Q.4  How do you add a column to a existing table? Give an example.

Ans:  ALTER TABLE Department ADD (AGE, NUMBER);

Q.5  Define View?

Ans:  A View is a database object that is a logical representation of a table.

A view does not represent any physical data.
It is derived from a table but it has no longer of its own and often may be used in the same manner as a table.
A view is a virtual table that has columns as in a table.

Q.6  Can one drop a column from a table?If yes give an example

Ans:  YES, to delete a column in a table, use  ALTER TABLE table_name DROP COLUMN column_name

Q.7  Compare and contrast TRUNCATE and DELETE commands for a table.

Ans:  Both the command have the common outcome of getting rid of all rows in a table. The difference between these two command is that the “truncate” command is a DDL operation and it just moves high water mark and produce a now

Q.8 What is cursors?

Ans: Cursor is a database object used by applications for manipulating data in a set on a row-by-row basis, instead of typical SQL commands which operate on all the rows in set at one time.

Q.9 What’s the difference between a primary key and a unique key? Explain.

Ans: Both primary key and unique enforce uniqueness of column on which they are defined. But by default primary key creates a clustered index on column, while unique creates a non-clustered index by default. Major difference is that, primary key does not allow NULLs while unique key allows one NULL only.

Q.10 What are Joins?

Ans: A Join combines columns and data from two or more tables (and in some cases, of one table with itself).

Q.11 How will you define SQL?

Ans: Structured query language(SQL) is the standard command set used for communicating with the relational database management system(RDBMS).

Q.12 Define DBMS?

Ans: A Database Management system(DBMS) consists of a collection of interrelated data and set of programs for accessing that data

Q.13 What is the different between Security and Integrity? Explain it.

Ans: Security is a protection from malicious attempts to modify or steal data.While the integrity constraints guard against any accidental damage to database, by ensuring that authorized changes to database will not result in a loss of data consistency.

Hope these question and answers will increase your knowledge in SQL.

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Q. 1 Define Normalisation?

Ans:  Normalisation is an essential part of database design. A good knowledge of the semantic of data helps the designer in designing an efficient design using all concept of normalization.

Q.2  What is the different between Security and Integrity? Explain it.

Ans:  Security is a protection against malicious attempts to steal or modify data. On the other hand integrity constraints guard against accidental damage to database. It ensure that authorized changes to database may not result in a loss of any data consistency.

Q. 3  What are the purpose of Normalisation?

Ans: Main purpose of Normalisation are as follows :
Minimize redundancy in data.
Remove insert, delete and update anomaly during the database activities.
Reducing the need to reorganize data it is enhanced or modified.

Q.4  How will you implement one-to-one, one-to-many and many-to-many relationships while designing tables?

Ans: One-to-One relationship is implemented as a single table. Sometimes is is also implemented as two tables with foreign and primary key relationships. One-to-Many relationships can be implemented by splitting data into two different tables with primary and foreign key relationships. Many-to-Many relationships can be implemented using a junction table with keys from both tables forming composite primary key of junction table.

Q. 5  How can you create a column alias?

Ans:  The ‘AS’ keyword is optional when specifying a column alias.

Q. 6  What is SubQuery?

Ans:  Subquery is the nesting of Queries within other query.

Q. 7  How can you hide definition of a stored procedure from a user ?

Ans: When we create stored procedure we use WITH ENCRYPTION. It will convert original statement of CREATE PROCEDURE into an encrypted format.

Q. 8  How can you disable a triger? Explain how.

Ans:  You can disable a single trigger in database by using  “DISABLE TRIGGER triggerName ON <<TableName>>” you can disable all the trigger with the use of “DISABLE Trigger ALL ON ALL SERVER”

Q. 9  What is functional dependency.

Ans:  Functional dependency tells that how one object depends upon the other object in the database.

Q. 10  Define Inner Join.

Ans: An inner Join is the default type of join in Query and View Designer.An inner Join is join that displays only rows that have common in both joined tables.

Q. 11  What are the different types of subquery?

Ans:

1. Single row subquery
2. Multiple row subquery
3. Correlated row subquery

Q. 12  What are the different types of replication?

Ans:    The SQL Server 2000-supported replication types are as follows :

1. Transactional
2. Snapshot
3. Merge

Q. 13  Explain the advantages of using Views ?

Ans:  Advantages of using views are as follows:

1. View provide simplify commands for the users.
2. View hide data complexity from user.
3. View stores complex queries.
4. View presents data in a different from that of the base table.
5. Views provides an additional level for table security.
6. View restrict access to a predetermined set of rows and columns of table.
7. View display only selective columns from a table.
8. Views provide groups of users access to data according to selected criteria.
9. Views provide data independence for application programs and ad hoc users.
10. A view can be used for retrieving data from multiple tables.

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Here we are giving some common SQL server questions with answers. These are frequently asked in project viva and also in job interview.

Here are some SQL Server Interview Questions

Q.1  What is use of GROUP BY and HAVING clause in SQL?

Ans:  The GROUP BY clause partitions the selected rows on distinct values of the column on which the group by has been made  while  HAVING selects groups which match the criteria specified.

Q.2  What is tuple in SQL?

Ans:  It is an instance of data within a relational database.

Q. 3  Explain SQL Profiler?

Ans: SQL Profiler is a graphical tool.  System administrators can monitor events in an instance of Microsoft SQL Server. We can save and capture data of each event in a file or SQL Server table and analyze it later.

Q. 4 Explain User Defined Functions?

Ans: User-Defined Functions allow us to define its own T-SQL functions. These function accept 0 or multiple parameters.

Q.5  What is schema?

Ans: It is a collection of database objects of Use.

Q.6  What is Sequence?

Ans: A Sequence is a database object. A Sequence may be used for providing very quick generation of unique numbers.

Q.7  What is Equi Joins in SQL?

Ans:  In this kind of join operation the join comparison operator is an equality. When we join two tables together through equality or values in one or more columns , this is called Equi join.

Q. 8 What is Cartesian Join?

Ans: When two tables are joined without using a where class it produces a Cartesian join. It combines each row of one table with each row of another table.

Q.9 Tell three SQL keywords which are used to change or set someone’s permissions?

Ans:  GRANT, REVOKE and  DENY.

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Q.10  What are data model in SQL?

Ans: Data model is the underlying the structure of the database.

Q.11 What is an Entity?

Ans:  Entity is a ‘thing’ in the real world and which has an independent existence.

Q.12  Explain Data Warehousing?

Ans: “A Data warehouse is a subject oriented, non volatile integrated ,time variant  collection of data for supporting management in decision making process”.

Q.13  Tell the advantages of Database?

Ans:

•     reduced data Redundancy
•     Shared data
•     Enforce security
•     Enforce security
•     Maintain integrity
•     Avoided data Inconsistency

Q.14  List the advantage of SQL?

Ans:

•     SQL provides a greater abstraction in comparison to procedural  languages.
•     End users and system personnel can deal with a number of database management system

Q.15 What is BCP?

Ans:  BCP is a short form of BulkCopy. We can copy heavy amount of data from table and view by using it.

Q.16  List some transaction properties?

Ans:

•     Durability
•     Atomicity
•     Consistency
•     Isolation

Q.17  Deference between DBMS and object oriented DBMS?

Ans:  DBMS contains a collection of interrelated data and also a set of program for accessing this data. While the object oriented DBMS stores information in the form of objects.

Q.18 List the types of SQL Commands?

Ans:

•     Data Control Language (DCL)
•     Data Manipulation Language (DML)
•     Data Definition Language (DDL)
•     Data Query Language (DQL)

Q.19 What are attributes in SQL?

Ans:  In SQL an entity is represented by a set of attributes. These are descriptive properties of each member of an entity set. Different types of attributes are.

•     Composite
•     Single-valued
•     Simple
•     Derived

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