SQL server Interview Questions

What is SQL?

A.SQL stands for Structured Query Language , and it is used to communicate with the Database. This is a standard language used to perform tasks such as retrieval, updating, insertion and deletion of data from a database.

What is denormalization and when would you go for it?

It is the reverse process of normalization. It increases query performance by reducing the joins. It is used for OLAP applications.

Difference between sp (stored procedure) and fn(function)?

Procedures can return as zero or null values.Function can reform one value which is mandatory.
procedures can have input ,output parameters.Fn can have only input parameters
procedure allows’select’ as well as DML statement in it.Fn allows only select statement.
Function can be called from procedures.Procedure cannot be caused from fn.
Exception can be handeled by try-catch block in a procedure.Try catch block cannot be used in a fn.
We can go for transaction mgmt in procedure.We can’t go for tranx mgmt.
Procedures cannot be utilized in a select statement.Function can be utilized in select statement.

SQL server Interview Questions

Difference between Delete and truncate?

Delete is used to delete rows from table.Truncate is used to delete all rows from table and free the space containing table.
Its DML command.Its DDL command.
We can use where condition.Cannot use where condition.
Can activate trigger because the operation are logged individually.Cannot activate trigger the operation doesn’t individual row deletion.
slower than truncate.Faster in performance.
Rollback is possible.Rollback not possible.

What is normalization? Explain different levels of normalization?

It is the way to eliminate redundant data

Reduces null value
Enables efficient indexing
1NF – Removes duplicated attributes, Attribute data should be atomic, and attribute should be the same kind.
2NF – Should be in 1NF and each non-key is fully dependent on the primary key.
3NF – Should be in 2NF and all the non-key attributes which are not dependent on the primary key should be removed. All the attributes which are dependent on the other non-key attributes should also be removed. Normalization is done in.

What is a Database?

“Database is nothing but an organized form of data for easy access, storing, retrieval and managing of data. This is also known as structured form of data which can be accessed in many ways.

Example: School Management Database, Bank Management Database.”

Advance SQL server Interview Questions

What are tables and Fields?

“A table is a set of data that are organized in a model with Columns and Rows. Columns can be categorized as vertical, and Rows are horizontal. A table has specified number of column called fields but can have any number of rows which is called record.


Table: Employee.

Field: Emp ID, Emp Name, Date of Birth.”

What is a primary key?

A primary key is a combination of fields which uniquely specify a row. This is a special kind of unique key, and it has implicit NOT NULL constraint. It means, Primary key values cannot be NULL.

What is a unique key?

“A Unique key constraint uniquely identified each record in the database. This provides uniqueness for the column or set of columns.

A Primary key constraint has automatic unique constraint defined on it. But not, in the case of Unique Key.

There can be many unique constraint defined per table, but only one Primary key constraint defined per table.”

SQL server Interview Questions

What is a foreign key?

A foreign key is one table which can be related to the primary key of another table. Relationship needs to be created between two tables by referencing foreign key with the primary key of another table.

What is a join?

This is a keyword used to query data from more tables based on the relationship between the fields of the tables. Keys play a major role when JOINs are used.

What is a View?

A view is a virtual table which consists of a subset of data contained in a table. Views are not virtually present, and it takes less space to store. View can have data of one or more tables combined, and it is depending on the relationship.

Advance SQL server Interview Questions

What is an Index?

An index is performance tuning method of allowing faster retrieval of records from the table. An index creates an entry for each value and it will be faster to retrieve data.

What are all the different types of indexes?

“There are three types of indexes -.

Unique Index.
This indexing does not allow the field to have duplicate values if the column is unique indexed. Unique index can be applied automatically when primary key is defined.

Clustered Index.
This type of index reorders the physical order of the table and search based on the key values. Each table can have only one clustered index.

Non Clustered Index.
Non Clustered Index does not alter the physical order of the table and maintains logical order of data. Each table can have 999 non clustered indexes.”

What is a Cursor?

A database Cursor is a control which enables traversal over the rows or records in the table. This can be viewed as a pointer to one row in a set of rows. Cursor is very much useful for traversing such as retrieval, addition and removal of database records.

SQL server Interview Questions

What is a relationship and what are they?

“Database Relationship is defined as the connection between the tables in a database. There are various data basing relationships, and they are as follows:.

One to One Relationship.
One to Many Relationship.
Many to One Relationship.
Self-Referencing Relationship.”

What is a stored procedure?

Stored Procedure is a function consists of many SQL statement to access the database system. Several SQL statements are consolidated into a stored procedure and execute them whenever and wherever required.

What is a trigger?

“A DB trigger is a code or programs that automatically execute with response to some event on a table or view in a database. Mainly, trigger helps to maintain the integrity of the database.

Example: When a new student is added to the student database, new records should be created in the related tables like Exam, Score and Attendance tables”

TRUNCATE removes all rows from the table. Truncate operation cannot be rolled back.”

Advance SQL server Interview Questions

What are local and global variables and their differences?

“Local variables are the variables which can be used or exist inside the function. They are not known to the other functions and those variables cannot be referred or used. Variables can be created whenever that function is called.

Global variables are the variables which can be used or exist throughout the program. Same variable declared in global cannot be used in functions. Global variables cannot be created whenever that function is called.”

What is a constraint?

“Constraint can be used to specify the limit on the data type of table. Constraint can be specified while creating or altering the table statement. Sample of constraint are.


What is data Integrity?

Data Integrity defines the accuracy and consistency of data stored in a database. It can also define integrity constraints to enforce business rules on the data when it is entered into the application or database.

SQL server Interview Questions

What is Auto Increment?

“Auto increment keyword allows the user to create a unique number to be generated when a new record is inserted into the table. AUTO INCREMENT keyword can be used in Oracle and IDENTITY keyword can be used in SQL SERVER.

Mostly this keyword can be used whenever PRIMARY KEY is used.”

What is the difference between Cluster and Non-Cluster Index?

“Clustered index is used for easy retrieval of data from the database by altering the way that the records are stored. Database sorts out rows by the column which is set to be clustered index.

A non clustered index does not alter the way it was stored but creates a complete separate object within the table. It point back to the original table rows after searching.”

What is Data warehouse?

Data warehouse is a central repository of data from multiple sources of information. Those data are consolidated, transformed and made available for the mining and online processing. Warehouse data have a subset of data called Data Marts.

Advance SQL server Interview Questions

What is Self-Join?

Self-join is set to be query used to compare to itself. This is used to compare values in a column with other values in the same column in the same table. ALIAS ES can be used for the same table comparison.

What is Cross-Join?

Cross join defines as Cartesian product where number of rows in the first table multiplied by number of rows in the second table. If suppose, WHERE clause is used in cross join then the query will work like an INNER JOIN.

What is user defined functions?

User defined functions are the functions written to use that logic whenever required. It is not necessary to write the same logic several times. Instead, function can be called or executed whenever needed.

SQL server Interview Questions

What are all types of user defined functions?

“Three types of user defined functions are.

Scalar Functions.
Inline Table valued functions.
Multi statement valued functions.
Scalar returns unit, variant defined the return clause. Other two types return table as a return.”

Advantages and Disadvantages of Stored Procedure?

“Stored procedure can be used as a modular programming – means create once, store and call for several times whenever required. This supports faster execution instead of executing multiple queries. This reduces network traffic and provides better security to the data.

Disadvantage is that it can be executed only in the Database and utilizes more memory in the database server.”

What is Online Transaction Processing (OLTP)?

“Online Transaction Processing (OLTP) manages transaction based applications which can be used for data entry, data retrieval and data processing. OLTP makes data management simple and efficient. Unlike OLAP systems goal of OLTP systems is serving real-time transactions.

Example – Bank Transactions on a daily basis.”

Advance SQL server Interview Questions

What is CLAUSE?

“SQL clause is defined to limit the result set by providing condition to the query. This usually filters some rows from the whole set of records.

Example – Query that has WHERE condition

Query that has HAVING condition.”

What is recursive stored procedure?

A stored procedure which calls by itself until it reaches some boundary condition. This recursive function or procedure helps programmers to use the same set of code any number of times.

What is Union, minus and Interact commands?

“UNION operator is used to combine the results of two tables, and it eliminates duplicate rows from the tables.

MINUS operator is used to return rows from the first query but not from the second query. Matching records of first and second query and other rows from the first query will be displayed as a result set.

INTERSECT operator is used to return rows returned by both the queries.”

SQL server Interview Questions

What is an ALIAS command?

“ALIAS name can be given to a table or column. This alias name can be referred in WHERE clause to identify the table or column.


Select st.StudentID, Ex.Result from student st, Exam as Ex where st.studentID = Ex. StudentID
Here, st refers to alias name for student table and Ex refers to alias name for exam table.”

What is the difference between TRUNCATE and DROP statements?

TRUNCATE removes all the rows from the table, and it cannot be rolled back. DROP command removes a table from the database and operation cannot be rolled back.

What are aggregate and scalar functions?

“Aggregate functions are used to evaluate mathematical calculation and return single values. This can be calculated from the columns in a table. Scalar functions return a single value based on the input value.

Example -.

Aggregate – max(), count – Calculated with respect to numeric.

Scalar – UCASE(), NOW() – Calculated with respect to strings.”

Advance SQL server Interview Questions

How can you create an empty table from an existing table?

“Example will be -.

Select * into student copy from student where 1=2
Here, we are copying student table to another table with the same structure with no rows copied.”

How to fetch common records from two tables?

“Common records result set can be achieved by -.

Select studentID from student INTERSECT Select StudentID from Exam”

How to fetch alternate records from a table?

“Records can be fetched for both Odd and Even row numbers -.

To display even numbers-.

Select studentId from (Select rowno, studentId from student) where mod(rowno,2)=0
To display odd numbers-.

Select studentId from (Select rowno, studentId from student) where mod(rowno,2)=1
from (Select rowno, studentId from student) where mod(rowno,2)=1.[/sql]”

SQL server Interview Questions

How to select unique records from a table?

“Select unique records from a table by using DISTINCT keyword.

Select DISTINCT StudentID, StudentName from Student.”

What is the command used to fetch first 5 characters of the string?

“There are many ways to fetch first 5 characters of the string -.

Select SUBSTRING(StudentName,1,5) as studentname from student
Select LEFT(Studentname,5) as studentname from student”

Which operator is used in query for pattern matching?

“LIKE operator is used for pattern matching, and it can be used as -.

% – Matches zero or more characters.
_(Underscore) – Matching exactly one character.
Example -.

Select * from Student where studentname like ‘a%’
Select * from Student where studentname like ‘ami_'”

Advance SQL server Interview Questions

What is RDBMS? How is it different from DBMS?

RDBMS stands for Relational Database Management System. The key difference here, compared to DBMS, is that RDBMS stores data in the form of a collection of tables and relations can be defined between the common fields of these tables. Most modern database management systems like MySQL, Microsoft SQL Server, Oracle, IBM DB2 and Amazon Redshift are based on RDBMS.

What is the difference between SQL and MySQL?

SQL is a standard language for retrieving and manipulating structured databases. On the contrary, MySQL is a relational database management system, like SQL Server, Oracle or IBM DB2, that is used to manage SQL databases.

What are Tables and Fields?

A table is an organized collection of data stored in the form of rows and columns. Columns can be categorized as vertical and rows as horizontal. The columns in a table are called fields while the rows can be referred to as records.

SQL server Interview Questions

What are Constraints in SQL?

“Constraints are used to specify the rules concerning data in the table. It can be applied for single or multiple fields in an SQL table during creation of table or after creation using the ALTER TABLE command. The constraints are:

NOT NULL – Restricts NULL value from being inserted into a column.
CHECK – Verifies that all values in a field satisfy a condition.
DEFAULT – Automatically assigns a default value if no value has been specified for the field.
UNIQUE – Ensures unique values to be inserted into the field.
INDEX – Indexes a field providing faster retrieval of records.
PRIMARY KEY – Uniquely identifies each record in a table.
FOREIGN KEY – Ensures referential integrity for a record in another table.”

What is a Primary Key?

“The PRIMARY KEY constraint uniquely identifies each row in a table. It must contain UNIQUE values and has an implicit NOT NULL constraint.
A table in SQL is strictly restricted to have one and only one primary key, which is comprised of single or multiple fields (columns).

CREATE TABLE Students ( /* Create table with a single field as primary key */
Name VARCHAR(255)

CREATE TABLE Students ( /* Create table with multiple fields as primary key */
LastName VARCHAR(255)
FirstName VARCHAR(255) NOT NULL,

ALTER TABLE Students /* Set a column as primary key */

ALTER TABLE Students /* Set multiple columns as primary key / ADD CONSTRAINT PK_Student /Naming a Primary Key*/
PRIMARY KEY (ID, FirstName);”

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