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SQL Server Interview Questions

Are you preparing for an SQL Server interview? Preparing for a SQL Server interview requires a comprehensive understanding of SQL concepts, ranging from basic to advanced levels. Whether you’re a seasoned professional or a beginner, it’s essential to review and practice common interview questions to ensure readiness.

In this interview preparation guide, we’ll cover a range of SQL Server interview questions categorized by difficulty level, from easy to advanced, including query-based questions. From explaining fundamental SQL Server concepts to tackling complex query scenarios, this comprehensive resource will help you ace your SQL Server interview.



Top 50 SQL Server Interview Questions for 2024

The questions are categorized in the four levels:



Beginner SQL Server Interview Questions

Preparing for your initial SQL Server interview? Gain confidence by mastering foundational concepts. This guide explores frequently asked beginner questions on database creation, querying techniques, and table management.

1. Explain the Difference Between SQL and T-SQL.

Basis of Comparison

SQL

T-SQL

Stands For

Structured Query Language

Transact – SQL

Definition

Used for querying and manipulating data stored in a database.

It’s an extension of SQL that is primarily used in Microsoft SQL Server databases and software.

Feature

SQL is open-source.

T-SQL is developed and owned by Microsoft.

Functions

Basic functions provided by SQL standards

Additional functions provided by Microsoft SQL Server

Triggers

Supported, but specifics may vary between database systems

Supported, with specific syntax and features in Microsoft SQL Server

Error Handling

Basic error handling capabilities provided by SQL standards

Enhanced error handling features available in T-SQL

2. What are the Different Data Types Used in SQL Server?

In SQL Server, there are several data types used to define the type of data that can be stored in a column. Here are some of the commonly used data types:

  1. Numeric Data Types
  2. Character String Data Types
  3. Date and Time Data Types
  4. Binary Data Types
  5. Boolean Data Type
  6. Other Data Types
    1. XML
    2. JSON
    3. HIERARCHYID

3. How to Create a Table in SQL Server?

To create a table in SQL Server, you can use the CREATE TABLE statement followed by the table name and a list of column definitions.

CREATE TABLE TableName (
    Column1 DataType1 [Constraint],
    Column2 DataType2 [Constraint],
    ...
    ColumnN DataTypeN [Constraint]
);

In addition, we can directly create the table using SQL Server Management Studio (SSMS).

4. What is the Purpose of an Alias in a Query?

In SQL Server, an alias is used to provide an alternative name for a table or a column in a query result set. The primary purposes of using aliases in a query are:

5. What is the Difference Between INNER JOIN and LEFT JOIN?

In SQL Server, INNER JOIN and LEFT JOIN are both types of join operations used to retrieve data from multiple tables based on a specified condition.

INNER JOIN

LEFT JOIN

6. How to Insert, Update, and Delete Data From a Table?

Insert Data: To insert data into a table, you use the INSERT INTO statement

INSERT INTO table_name (column1, column2,...) 
VALUES (value1, value2,...);

Update Data: To update existing data in a table, you use the UPDATE statement

UPDATE TableName
SET Column1 = NewValue1, Column2 = NewValue2, ...
WHERE Condition;

Delete Data: To delete data from a table, you use the DELETE FROM statement

DELETE FROM TableName
WHERE Condition;

7. How to Grant Permissions to a User?

In SQL Server, you can grant permissions to a user using the GRANT statement. Permissions can be granted at various levels such as database level, schema level, table level, and even specific stored procedures or functions.

GRANT permission_type 
ON [target] 
TO user_name;

we can also grant permission using SQL Server Management Studio.

8. How to Create a Stored Procedure?

To create a stored procedure in SQL Server, we can use the CREATE PROCEDURE statement followed by the procedure name and its definition. 

CREATE PROCEDURE procedure_name
    @parameter1 data_type,
    @parameter2 data_type,
    ...
AS
BEGIN
    -- SQL statements
END;

9. What are the Basic Aggregate Functions?

In SQL Server, aggregate functions are used to perform a calculation on a set of values and return a single value. Here are some of the basic aggregate functions:

  1. COUNT(): This function counts the number of rows in a result set or the number of non-null values in a column.
  2. MAX(): This function returns highest value in a column.
  3. MIN(): This function returns lowest value in a column.
  4. SUM(): This function returns the sum of all values in a numeric column.
  5. AVG(): This function calculates the average value of a numeric column.

10. How to Use the LIKE Operator for Pattern Matching?

In SQL Server, the LIKE operator is used for pattern matching in string values. It allows you to search for strings that match a specified pattern, which may include wildcard characters.

SELECT column1, column2, ...
FROM table_name
WHERE column_name LIKE pattern;

11. What is the Difference Between a Scalar Function and a Table-Valued Function?

Scalar Function

Table-valued Functions

12. Explain the Basic Concept of User-Defined Functions (UDFs).

We can use UDFs for the following reasons:

  1. They can be created, stored, and called at any number of times.
  2. They allow faster execution because UDFs don’t need to be reparsed or reoptimized.
  3. They minimize network traffic as it reduces the number of rows sent to the client.

13. How to Check the Execution Plan of a Query?

  1. On the toolbar, select Database Engine Query. we can also open an existing query and display the estimated execution plan by selecting the Open File toolbar button and locating the existing query.
  2. Enter the query for which we would like to display the estimated execution plan.
  3. On the Query menu, select Display Estimated Execution Plan or select the Display Estimated Execution Plan toolbar button. The estimated execution plan is displayed on the Execution Plan tab in the results pane.

Display Estimated Execution

14. Explain the Difference Between Clustered and Non-Clustered Indexes.

Feature

Clustered Index

Non – Clustered Index

Definition

It describes the order in which data is stored in tables physically.

It doesn’t sort tables physically inside a table but creates a logical order for stored data.

Key Structure

Contains the actual data rows.

Contains only pointers to the data rows

Index Key Columns

Each table will have only one clustered index.

There could be many non-clustered indexes for a table.

Data Accessing

Fast

Slow

15. When would We Create an Index?

We would typically create an index to improve the performance of queries that frequently search or filter data based on certain columns.

Intermediate SQL Server Interview Questions

This section delves into commonly encountered interview questions for intermediate users. Test your knowledge on topics like joins, functions, and performance optimization to impress your interviewer.

16. How to Determine If an Index is Effective?

17. Can We Write a Query to find Unused Indexes?

We can find unused indexes by querying the dynamic management views (DMVs) provided by SQL Server. Here’s a query to find unused indexes:

SELECT
    OBJECT_NAME(s.[object_id]) AS TableName,
    i.name AS IndexName,
    i.type_desc AS IndexType,
    s.user_seeks,
    s.user_scans,
    s.user_lookups,
    s.user_updates
FROM
    sys.dm_db_index_usage_stats AS s
INNER JOIN
    sys.indexes AS i ON s.[object_id] = i.[object_id] AND s.index_id = i.index_id
WHERE
    OBJECTPROPERTY(s.[object_id],'IsUserTable') = 1
    AND s.database_id = DB_ID()
    AND (s.user_seeks + s.user_scans + s.user_lookups) = 0
ORDER BY
    TableName,
    IndexName;

This query retrieves information about indexes along with their usage statistics. Unused indexes will have NULL values for user seeks, scans, and lookups but non-NULL values for user updates.

18. What are the Benefits of using Views in SQL Server?

19. How to Create a View with Joins and Aggregates?

Here we have created a view named loss_summary_view with columns week, from_code, to_code, count_a, sum_x, sum_y, and sum_z. The view is constructed by selecting data from tables history and calendar and performing joins and aggregate functions.

CREATE VIEW loss_summary_view (week, from_code, to_code, count_a, sum_x, sum_y, sum_z)
AS 
SELECT c.week, h.from_code, h.to_code, COUNT(h.a) AS count_a, SUM(h.x) AS sum_x, SUM(h.y) AS sum_y, SUM(h.z) AS sum_z
FROM history AS h
JOIN calendar AS c ON c.month = 100610 AND c.day = h.day 
GROUP BY c.week, h.from_code, h.to_code;

20. How to Update Data through a View?

Create a view showing customers from Paris using the WITH CHECK OPTION statement.

CREATE VIEW vwCustomersParis
AS
 SELECT CompanyName, ContactName, Phone, City
 FROM Customers
 WHERE City = 'Paris'
WITH CHECK OPTION

Update the above created view by moving everyone from Paris to Lyons.

UPDATE vwCustomersParis
SET City = 'Lyons'

The above statement update data by moving everyone from Paris to Lyons will fail because Lyons does not meet the criteria defined in the view.

21. Explain the Security Implications of using Views.

22. How to Identify Performance Bottlenecks in a Query?

23. What are some Techniques for Query Optimization?

24. Explain the Role of Statistics in Query Optimization.

25. How can we Use Partitioning to Improve Performance?

26. Describe Different Authentication Modes in SQL Server.

In SQL Server, there are two different kinds of authentication modes:

27. How can we Implement Role-Based Access Control (RBAC) in SQL Server?

1. Identify Roles: Determine the roles needed for our application or system.

2. Create Database Roles: Use the CREATE ROLE statement to create database roles that correspond to the identified roles. 

CREATE ROLE SalesRole;
CREATE ROLE HRRole;

3. Assign Permissions to Roles: Grant appropriate permissions to each role using the GRANT statement. 

GRANT SELECT, INSERT, UPDATE, DELETE ON dbo.SalesTable TO SalesRole;
GRANT SELECT, INSERT, UPDATE, DELETE ON dbo.EmployeeTable TO HRRole;

4. Assign Users to Roles: Add users to the appropriate roles using the ALTER ROLE statement or the sp_addrolemember stored procedure.

ALTER ROLE SalesRole ADD MEMBER SalesUser;
EXEC sp_addrolemember 'HRRole', 'HRUser';

5. Use Role-Based Security: Modify our application or system to utilize role-based security. Instead of directly granting permissions to users, check their roles and grant permissions based on their roles. 

IF USER_IN_ROLE('SalesRole')
BEGIN
    -- Allow access to sales-related functionality
END
ELSE IF USER_IN_ROLE('HRRole')
BEGIN
    -- Allow access to HR-related functionality
END

28. What are Stored Procedures and How can they Improve Security?

Stored procedures in SQL Server are precompiled sets of SQL statements that can be reused.

Stored procedures can improve security in several ways:

29. Explain Different Types of Replication in SQL Server.

In SQL Server, three different types of replications are available:

30. When would we use Transactional Replication Versus Merge Replication?

Transactional Replication:

Merge Replication:

Advanced SQL Server Interview Questions

Elevate your interview preparation by deep diving into advanced SQL Server interview question section. Be ready to showcase your expertise with complex queries, performance optimization strategies, and intricate server administration tasks.

31. How do we Configure and Manage Replication in SQL Server?

Configuring and managing replication in SQL Server involves several steps. Here’s a general overview:

  1. Identify Publisher and Distributor.
  2. Choose replication type: Snapshot, Transactional, or Merge.
  3. Set up publication to specify data to replicate.
  4. Define subscriptions for where replicated data will be delivered.
  5. Monitor replication status and performance using SSMS or Replication Monitor.
  6. Handle maintenance tasks such as index maintenance and backup/restoration.

32. Explain Different High Availability Solutions in SQL Server (e.g., Always On Availability Groups).

Always On Availability Groups:

Failover Clustering:

Database Mirroring:

Log Shipping:

Replication:

33. How to Configure And Manage Always On Availability Groups?

Configuring and managing Always On Availability Groups (AGs) in SQL Server involves several steps. Here’s a general guide:

Always On Availability Groups provide high availability and disaster recovery solutions for SQL Server databases.

34. What are the Considerations For Disaster Recovery in SQL Server?

35. Can we Write a Script to Import Data from a Flat File into a Table in SQL Server?

Yes, we can write a script to import data from a flat file into a table in SQL Server. Here’s an example script using the BULK INSERT statement:

BULK INSERT TableName
FROM 'C:\Path\To\Your\File.csv'
WITH
(
    FIELDTERMINATOR = ',',  -- Specify the field terminator
    ROWTERMINATOR = '\n',    -- Specify the row terminator
    FIRSTROW = 2            -- Specify the first row to start importing data
);

In this script, replace TableName with the name of your SQL Server table and 'C:\Path\To\Your\File.csv' with the path to your flat file. Adjust FIELDTERMINATOR and ROWTERMINATOR as per your file format.

36. Explain how to Loop through a Result Set using Cursors in SQL Server.

To loop through a result set using cursors in SQL Server, you can follow these steps:

37. How can we use Error Handling in T-SQL scripts?

In T-SQL scripts, error handling can be implemented using the TRY…CATCH construct.

BEGIN TRY
    -- T-SQL statements that might raise an error
    -- For example:
    SELECT 1/0; -- This will raise a divide by zero error
END TRY
BEGIN CATCH
    -- Catch block to handle the error
    -- we  can capture information about the error using functions like ERROR_NUMBER(), ERROR_MESSAGE(), etc.
    PRINT 'An error occurred: ' + ERROR_MESSAGE(); -- Print the error message
    -- Additional error handling logic can be implemented here
END CATCH;

Functions like ERROR_NUMBER(), ERROR_MESSAGE(), ERROR_STATE(), ERROR_SEVERITY(), and ERROR_PROCEDURE() can be used to retrieve information about the error.

38. Explain the Basic Components of SSIS packages.

The important component in SSIS package are:

Query Based SQL Server Interview Questions

For our better understanding, we will considering the following tables to write queries.

Employee Table:

Employee Table

Departments Table:

Departments Table

Sales Table:

Sales Table

Order Table:

Order Table

39. Write a SQL Query to Find the nth Highest Salary from an Employee Table.

SELECT DISTINCT TOP 1 Salary AS NthHighestSalary
FROM (
    SELECT TOP 1 Salary
    FROM Employees
    ORDER BY Salary DESC
) AS NthHighestSalaries
ORDER BY Salary ASC;

Output:

Highest salary

40. Write a SQL Query to Retrieve the Names of Employees who are also Managers.

SELECT e.emp_name 
FROM Employees e 
JOIN Employees m ON e.manager_name = m.emp_name;

Output:

Output

41. Write a SQL Query to Find the Second Highest Salary from an Employee table.

SELECT MAX(Salary) AS salary 
FROM Employees 
WHERE Salary < (SELECT MAX(Salary) FROM Employees);

Output:

Second highest salary

42. Write a Query to Calculate the Total Number of Orders Placed by each Customer.(order table)

SELECT cust_ID, COUNT(*) AS TotalOrders 
FROM Orders 
GROUP BY cust_ID;

Output:

Output

43. Write a Query to Find Employees who have the Same Job Title but Different Salaries.

SELECT e1.emp_id , e1.emp_name, e1.JobTitle, e1.Salary 
FROM Employees e1 
JOIN Employees e2 ON e1.JobTitle= e2.JobTitle
WHERE e1.emp_id  <> e2.emp_id AND e1.Salary <> e2.Salary 
ORDER BY e1.job_title, e1.emp_id;

Output:

Output

44. Write a SQL Query to get the Top 5 Highest-Paid Employees.

SELECT TOP 5 * FROM Employees 
ORDER BY Salary DESC;

Output:

Output

45. Write a Query to Find All Employees who Joined in the Last Month.

SELECT * FROM Employees
WHERE JoinDate>= DATEADD(MONTH, -1, DATEADD(MONTH, DATEDIFF(MONTH, 0, GETDATE()), 0))
 AND JoinDate< DATEADD(MONTH, DATEDIFF(MONTH, 0, GETDATE()), 0);

Output:

No employees are there who joined in the last month.

Output

46. Write a SQL Query to Find Duplicate Records in a Table.

SELECT emp_name, COUNT(*) AS DuplicateCount 
FROM Employees 
GROUP BY emp_name 
HAVING COUNT(*) > 1;

Output:

Output

47. Write a Query to Calculate the Average Salary of Employees in Each Department.

SELECT d.dept_name, AVG(e.Salary) AS AvgSalary 
FROM Employees e 
JOIN 
Departments d ON e.dept_id = d.dept_id
GROUP BY d.dept_name;

Output:

Output

48. Write a SQL Query to Find the Total Number of Products Sold each month.

SELECT 
    YEAR, 
    MONTH, 
    COUNT(*) AS TotalProductsSold 
FROM 
    Sales 
GROUP BY 
    YEAR, 
    MONTH 
ORDER BY 
    YEAR, 
    MONTH;

Output:

Output

49. Write a SQL Query to Identify Employees who have Duplicate Manager Names.

SELECT e1.emp_ID, e1.emp_name, e1.manager_name FROM Employees e1
JOIN Employees e2 ON e1.manager_name = e2.manager_name
WHERE e1.emp_ID <> e2.emp_ID
AND e1.emp_name <> e2.emp_name
ORDER BY e1.manager_name, e1.emp_ID;

Output:

Output

50. Write a Query to Fetch the Names of Employees Along with their Department Names.

SELECT e.emp_name, d.dept_name 
FROM Employees e 
JOIN Departments d ON e.dept_ID = d.dept_ID;

Output:

Output

Conclusion

mastering SQL Server interview questions is crucial for anyone aspiring to excel in database management roles. By delving into the topics covered in this guide, from basic SQL concepts to advanced techniques like query optimization and replication, you’re equipping yourself with the knowledge needed to ace SQL Server interviews.

Keep practicing, stay updated with the latest advancements in SQL Server technology, and approach each interview with confidence. With a solid understanding of SQL fundamentals and hands-on experience, you’ll be well-prepared to impress potential employers and secure your desired role in the ever-evolving world of database management.

Frequently Asked Questions – SQL Server Interview Question

Q. How do I prepare for a SQL interview?

Brush up on SQL fundamentals, practice queries, explore advanced topics (if needed), and hone your interview skills.

Q. What are the jobs in SQL Server?

There are multiple jobs in SQL Server like: Data scientist, Business analyst, Quality assurance engineer, Server engineer and more.

Q. What are the benefits of using SQL Server?

Using SQL Server offers benefits such as data security, reliability, scalability, and integration with other Microsoft products and technologies. It also provides tools for data analysis, reporting, and business intelligence.

Q. How can I learn SQL Server?

You can learn SQL Server through online tutorials, official Microsoft documentation, virtual labs, and training courses. There are also community forums and user groups dedicated to SQL Server where you can learn from experienced professionals and enthusiasts.

Q. What are the latest features in SQL Server?

The latest versions of SQL Server include features such as in-memory OLTP, always encrypted, enhanced security capabilities, improved query processing, and better integration with cloud services.


Article Tags :
Databases
Interview Questions
SQL Server
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