In this article, we share the top 55 SQL server interview questions. If you want to land a job in SQL Server database administration, review these SQL server questions to sharpen your SQL skills and build your confidence ahead of your next SQL server interview.
And rather than focusing on the theory of SQL Server, we’ve also included a series of technical SQL server interview questions that allow you to demonstrate your SQL command abilities in a database admin role.
And when you factor in that the US Bureau of Labor Statistics reports a median salary of over $100,000 per year for database admins, you really need to stand out to land your dream position. The best way to do that is to demonstrate a well-rounded set of SQL Server skills.
By reviewing these SQL server interview questions and answers, you can have a stronger understanding of what to expect during your next SQL server interview and feel more confident in your ability to tackle any SQL server question that comes your way.
SQL Server Interview Questions for Beginners
1. What Is SQL Server?
This is one of the most basic ms SQL server interview questions, so it’s really essential to know it well.
That said, your interviewer is likely looking for you to share that SQL Server is a relational database management system (RDBMS) from Microsoft that’s used to store, process and secure data in a structured way. It also offers features like analysis, reporting, integration, master data management, and even machine learning.
2. What Are Foreign and Primary Keys in SQL Server?
This is one of those MSSQL interview questions where I can show my fundamental understanding of how primary and foreign keys differ. It’s also helpful to refer to any SQL projects I may have built to fully demonstrate my knowledge here.
That said, I would summarize the following:
- Primary key: Can be one column or a group of columns to uniquely identify table rows.
- Foreign key: This can also be one column or a group of columns that refers to the primary key from another. This is essential for referential integrity between tables in relational databases.
3. What Is a Clustered and Non-Clustered Index in SQL Server?
Clustered indexes are like a well-organized filing system for data. They determine the physical order of data in a table based on the primary key or a unique column. This makes retrieving information more efficient.
On the other hand, non-clustered indexes act as quick access paths for frequently queried columns. They don't affect the physical order of data but help locate specific information faster.
In a nutshell, clustered indexes bring order to data, while non-clustered indexes speed up data retrieval.
4. Explain What SQL Profiler Is.
This handy SQL Server tool captures and analyzes SQL Server events, enabling database administrators and developers to monitor SQL Server activities, including executed queries, stored procedures, and error reports.
5. What Are Normalization and Denormalization in SQL Server?
Normalization involves breaking a large table into smaller tables and establishing relationships using foreign keys to minimize data redundancy and dependency.
Denormalization is the opposite process, and it involves adding redundant data to a normalized database to improve query performance. This is because it excludes the need for expensive joins or subqueries.
6. What Is An Index In SQL Server, And How Does It Improve Query Performance?
This is another of those relatively simple questions on SQL server that you need to know well.
Your interviewer would like to hear that this is a database structure that uses keys and pointers to locate and access data quickly. By creating indexes on columns that are frequently used, SQL Server can avoid scanning the entire table and perform efficient index seeks or scans, which leads to faster query performance.
7. What Is a Transaction in SQL Server?
This is a logical unit of one or more database operations that are executed together to maintain consistency and integrity. Transactions ensure data integrity by allowing multiple changes to be made as a single atomic operation.
8. How Does a Stored Procedure Improve Performance in SQL Server?
It improves performance by being pre-compiled, optimized for performance, reducing network traffic, and enhancing security.
9. How Would You Define a Trigger in an SQL Server? And List The Types of Triggers.
This is a special type of database object that contains a set of SQL statements that are automatically executed after specific data manipulation events like INSERT, UPDATE, or DELETE.
The different types of triggers in SQL Server are:
- DML triggers for data manipulation
- DDL triggers for data definition
- CLR triggers for executing CLR code
- Logon triggers for user logins
- Database triggers for database-level events.
10. What Is A Cursor In SQL Server, And When Would You Use It?
It is a database object used to retrieve and manipulate data from a result set one row at a time. It is used in situations where complex data manipulations cannot be easily accomplished with a single SQL statement. For instance:
- When iterating through a result set and performing calculations or transformations on each row individually
- Updating or deleting rows based on complex criteria
- Processing data in a specific order
- Performing multiple operations on a single row of data before moving to the next row.
11. How Would You Define the CHECK Constraint In SQL Server?
As with all types of constraints, the CHECK constraint is used to specify rules for the data in a table. It is a type of constraint that ensures a condition is met before a row can be inserted or updated in a table.
This condition is defined using a Boolean expression that evaluates to TRUE or FALSE and can reference one or more columns in the table.
12. What Is a Subquery in SQL Server, And How Does It Differ From A Regular Query?
A subquery is a nested query that is used to retrieve data for the main query. It is enclosed in parentheses and typically appears within a WHERE or HAVING clause.
A subquery differs from a regular query because it is nested within another query, while a regular query stands alone.
13. Mention The Most Common Types Of Queries In SQL Server.
With this question, you can show that you’re aware of various types of SQL command, such as DDL, DML, DCL, TCL, and DQL. You can then mention the most common types of query:
- SELECT query: retrieves data from one or more tables.
- INSERT query: inserts new rows of data into a table.
- UPDATE query: modifies existing rows of data in a table.
- DELETE query: removes rows of data from a table.
- MERGE query: combines insert, update, or delete operations on a table based on join results with another table.
14. When Would You Use A CTE (Common Table Expression) In SQL Server?
Here are some common scenarios where you might use a CTE:
- Recursive Queries: a situation where a recursive query is necessary to navigate through hierarchical data structures (e.g., organizational charts or bill of materials).
- Simplifying Complex Queries: When faced with complex queries, CTEs can simplify these by enhancing readability and maintainability.
- Reusing Subqueries: If you need to reference a subquery multiple times within a larger query, a CTE can help you define the subquery once and refer to it multiple times.
15. What Is The Difference Between A Temporary Table And A Table Variable In SQL Server?
Stored in the tempdb database
Stored in memory
Can be created and dropped like regular tables
Automatically dropped at the end of the scope of the query or stored procedure
Can have indexes and constraints
Cannot have indexes or constraints, but can have primary keys
Can be used by multiple users and sessions
Can only be used by the session that created it
Can store large amounts of data
Can store small amounts of data
Can be used with SELECT INTO to create a new table based on the results of a query
Cannot be used with SELECT INTO to create a new table based on the results of a query
16. What Is A Full-Text Index And How Does It Work In SQL Server?
A full-text index is a specialized type of index that breaks text into words or terms and creates an index structure to map them to corresponding rows. These are great ways to improve search performance as they offer fast and accurate data based on textual content.
17. Explain What Scheduled Tasks Refer To In SQL Server.
Scheduled tasks are automated jobs or processes that run at specific times or intervals. These tasks can include various activities like executing stored procedures, running scripts or queries, performing database maintenance, and more.
SQL Server also provides a built-in scheduling system called SQL Server Agent which you can use to create and manage scheduled tasks. This is a great way for administrators to automate routine database operations and optimize system performance.
18. What Is The Method For Handling Exceptions In SQL Server Programming?
The TRY-CATCH block is essential for managing exceptions gracefully. As a developer, it allows you to define code that might throw an exception within a "try" block and subsequently manage any resulting exceptions in a corresponding "catch" block.
In the catch block, it is possible to analyze the exception and execute relevant actions, such as logging an error message or undoing a transaction. For more intricate error-handling situations, the TRY-CATCH block can also be nested.
Intermediate SQL Server Interview Questions
19. How Would You Define Bulkcopy In SQL Server?
Bulkcopy, also known as bulk data copy, refers to the ability to transfer large amounts of data between databases or between a database and an external data source quickly and efficiently. This is done with the Bulk Copy Program (BCP).
20. What Is Dynamic SQL, And When Would You Use Dynamic SQL In SQL Server?
This is the ability to construct and execute SQL statements dynamically at runtime, which is useful when the SQL statement isn't known at compile time. Some common use cases for dynamic SQL include:
- Dynamic filtering: When filtering conditions need to be determined dynamically based on user inputs or variable conditions.
- Dynamic table or column names: When table or column names need to be determined dynamically, such as when working with flexible schemas.
- Dynamic pivot or unpivot operations: When the number or names of columns for pivoting or unpivoting need to be determined dynamically.
- Dynamic SQL generation: When the SQL statements themselves need to be generated dynamically based on certain conditions or rules.
21. How Would You Delete A Table Using SQL Server Management Studio?
To delete a table in SQL Server Management Studio, follow these steps:
- Open SQL Server Management Studio and connect to the server that contains the database with the table you want to delete.
- Expand the Databases folder to display a list of databases on the server.
- Expand the database that contains the table you want to delete.
- Expand the Tables folder to display a list of tables in the database.
- Right-click the table you want to delete and select Delete from the context menu.
- A dialog box will appear, asking you to confirm the deletion. If you are sure you want to delete the table, click OK.
- The table will be deleted from the database.
22. What Is A Deadlock In SQL Server How Can You Prevent It?
This occurs when two or more transactions or processes are waiting for each other to release locked resources. To prevent deadlocks, you can try the following:
- Use appropriate indexing to minimize locking and blocking.
- Minimize transaction duration to reduce the possibility of deadlock occurrence.
- Avoid long transactions that need multiple locks or to update multiple resources.
- Access resources in a consistent order, which reduces the likelihood of deadlocks.
- Implement a retry mechanism to handle deadlocks when they occur.
- Increase the lock timeout value to allow more time for a transaction to complete.
- Use snapshot isolation levels to avoid locks on tables and rows.
- Use stored procedures and transactions to manage concurrency.
23. What Are Defaults In SQL Server?
These are predefined values that are automatically assigned to a column when a new row is inserted into a table, provided that the column value is not specified during the insert operation.
24. What Is a Plan Guide in SQL Server, And When Would You Use It?
These are tools that guide the SQL Server Query Optimizer when choosing a specific execution plan for a query. This is used when you have identified a specific query that needs better performance and has determined that a different execution plan would be more efficient.
25. What Is a Trace Flag in SQL Server?
A trace flag is a feature in SQL Server that enables database administrators to control specific system behaviors to diagnose issues, tune performance, or activate particular functionalities.
26. What Is A Checkpoint In SQL Server, And Why Is It Important?
A checkpoint in SQL Server is a process that flushes modified pages from memory to disk, creating a recovery point in case of a system failure or crash. It is important because it ensures that committed transactions are durable and reduces recovery time.
27. Why Would You Use @@SPID In SQL Server?
@@SPID is a system function that you can use to return the Session ID (SPID) of the current user session since this is a unique identifier for each user. This can be useful for a range of situations, including:
- To identify the current user process executing a particular query or stored procedure.
- To monitor and troubleshoot performance by identifying SPIDs consuming resources.
- To terminate a specific user process that is causing problems with the KILL command.
28. How Would You Optimize A Slow-Running SQL Server Query?
Optimizing a slow-running SQL Server query involves identifying the performance bottlenecks and addressing them. Here are some ways to optimize a slow-running SQL Server query:
- Examine the query execution plan to identify performance bottlenecks like table scans, expensive joins, or missing indexes.
- Ensure appropriate indexes are used to support query filtering, sorting, and joining operations.
- Rewrite the query to simplify complex expressions by removing redundant joins or subqueries, using query restructuring or common table expressions (CTEs).
- Update statistics to ensure optimal query plans via the UPDATE STATISTICS command.
- Ensure sufficient resources are available to handle the query workload and monitor performance with SQL Server Profiler or Performance Monitor.
- Consider query caching if the query is executed frequently or use materialized views to precompute and store complex query results.
- Partitioning or data archiving can improve query performance by reducing the data volume accessed during query execution.
- Test the optimized query to ensure changes have resulted in improved performance.
29. How Do You Perform Pagination In SQL Server?
You have two options here, with the first being the OFFSET-FETCH clause and the second being the ROW_NUMBER() function, which also needs to use the ORDER BY and WHERE clauses.
Depending on your preference, OFFSET-FETCH fetches a range of rows, while ROW_NUMBER() assigns a unique integer to each row returned by the query.
30. Where Are Usernames And Passwords Stored In SQL Server?
Usernames and hashed passwords are stored in the "sys.sql_logins" system catalog view, which is a dynamic management view (DMV) in the "master" database. The passwords are not stored in clear text; instead, they are stored as a salted hash value for security purposes.
31. How Would You Determine The Size Of A SQL Server Database?
To determine the size of a SQL Server database, you can use the following methods:
- Use the "sp_spaceused" system stored procedure.
- Use the "sys.dm_db_partition_stats" dynamic management view
- Use the "sp_helpdb" system stored procedure to list databases and their size.
- Use SQL Server Management Studio to view the size of the database files and log files.
- Use the "sp_helpfile" system stored procedure to list all database files and their size.
32. What Is The Purpose Of The OVER() Clause In SQL Server?
The main purpose of the OVER() clause is to provide control over the scope of window functions. For example, you can partition rows into groups, specify the order of rows within each partition, and then apply window functions to these partitions.
This is really useful as it gives you flexibility when performing complex calculations and analysis over specific data subsets.
33. How Would You Define Magic Tables In SQL Server?
Magic tables are virtual tables that you can access within triggers to gain access to the inserted and deleted data from the DML operation. There are two types of magic tables:
- Inserted: Available in an INSERT trigger and contains the rows being inserted into the target table. It allows you to access the new data that triggered the insert operation.
- Deleted: Available in UPDATE and DELETE triggers and contains rows that are being updated or deleted from the target table, giving access to old data before modification.
34. What Is The Purpose Of The Database Engine Component In SQL Server?
The Database Engine is the core component of SQL Server, responsible for storing, processing, and securing data. It manages the data files, transactions, and security protocols for SQL Server databases.
35. How Do You Create An SQL Server Backup And Restore It?
To create a SQL Server backup and restore it, you can follow these general steps:
- Open SQL Server Management Studio and connect to the required database.
- Right-click on the database and select "Tasks" > "Back Up".
- In the "Back Up Database" window, choose backup type, destination, and backup options, then click "OK" to start the backup process
- To restore the database, right-click on the "Databases" node in Object Explorer and select "Restore Database".
- In the "Restore Database" window, select the source of the backup, the destination database name and location, and the restore options.
- Click "OK" to start the restore process.
36. What Is A Scalar Function In SQL Server?
This is a user-defined function that you can create with the CREATE FUNCTION statement, allowing you to return a single value based on input parameters.
37. What Are SQL Server Integration Services?
SQL Server Integration Services, or sometimes simply SSIS, is a component that’s used for building data integration and ETL solutions. With SSIS, you have access to standard ETL functions, along with workflow control, error handling, and scheduling.
38. How Do You Create A Stored Procedure In SQL Server?
To create a stored procedure, you can use the CREATE PROCEDURE statement followed by the name of the stored procedure, input parameters, and procedure logic, as shown in the code block below.
CREATE PROCEDURE proc_name
@param1 data_type = def_val,
@param_n data_type = def_val
-- Add logic and statements here
39. How Can You Handle Concurrency In SQL Server?
You actually have several ways to handle concurrency:
- Transactions are ideal for ensuring atomicity, consistency, isolation, and durability.
- Locking controls concurrent access to data and prevents conflicts.
- Optimistic concurrency is a great way to let multiple users access data simultaneously while also detecting conflicts when updating.
- Isolation levels can help to balance data consistency and concurrency.
40. What Is The XML Datatype In SQL Server?
The XML data type is useful for storing and manipulating XML data as it provides built-in functions for querying and transforming XML documents. This is ideal for enabling seamless integration and handling of hierarchical or semi-structured data in your database.
SQL Server Interview Questions For Experienced Professionals
41. Which Commands Can You Use To Create User-Defined Error Messages In SQL Server?
There are two ways you can do this. One way is to use the RAISERROR statement to raise a custom error message with a specified severity level, error number, and error message text.
RAISERROR('This is a custom error message.', 16, 1);
The other way is with the sp_addmessage procedure, which allows you to add a custom error message to the sys.messages catalog view. You can raise the error by referring to the error number and using the RAISERROR command.
EXEC sp_addmessage @msgnum = 50001, @severity = 16, @msgtext = 'This is a custom error message.';
42. Which Backup Types Are Used In SQL Server?
- Full backup: All data in the database
- Differential backup: All changes since the last full backup
- Transaction log backup: All logged transactions since the last transaction log backup
- File and filegroup backup: One or more database files or filegroups
- Partial backup: Specific filegroups and/or read-write filegroups within a database.
- Copy-only backup: Backup that doesn't affect the normal backup sequence, useful for creating ad-hoc backups without disrupting the backup chain.
43. What Is the Meaning of SSRS in SQL Server?
SSRS refers to SQL Server Reporting Services, which is a server-based reporting platform that you can use to create, manage, and deliver a wide range of reports for data analysis and decision-making.
44. What Is A Filtered Index In SQL Server?
This differs from a traditional index (which covers the entire table) because you can create this index on a specific subset of data that meets your filter criteria, resulting in a smaller index size and improved query performance.
45. What’s The Difference Between A Heap Table And A Clustered Index Table In SQL Server?
Heap Table: An unordered collection of rows stored in no particular order, and there is no concept of a primary key or clustered index. This means that data pages are not organized based on a key, and there is no defined order for fetching data.
Clustered Index Table: Has a defined data order that’s based on the clustered index key. This index determines the physical order of the data rows on disk, and each table can have only one clustered index, as this determines how data is stored and fetched from the table.
46. What Is a Parallel Execution Plan in SQL Server?
This is a type of query execution plan that makes use of parallelism across multiple threads or processors to execute queries concurrently.
47. What Are The Different Recovery Models In SQL Server?
- Simple Recovery Model: This is well suited for databases with lower recovery requirements as transaction logs are automatically truncated and log backups are not created.
- Full Recovery Model: This provides the highest level of data protection but requires regular log backups to manage log file sizes as it provides a complete transaction log backup and allows point-in-time recovery.
- Bulk-Logged Recovery Model: This is similar to full recovery, but it minimizes logging for certain large-scale operations like bulk data loads or index rebuilds. The trade-off here is that point-in-time recovery is not possible for these bulk operations.
48. What Is The Purpose Of The HASHBYTES Function In SQL Server?
The main purpose of the HASHBYTES function is to ensure data integrity and security, as it’s used to generate hash values for sensitive data like passwords. The HASHBYTES function also supports various hash algorithms like MD2, MD4, MD5, SHA-1, SHA-2, SHA-256, and more.
49. What Is Transparent Data Encryption (TDE) In SQL Server?
Transparent Data Encryption (TDE) provides encryption at the database level. This means that TDE encrypts the entire database, including data files, log files, and backups, to protect sensitive information at rest.
50. What Are The Benefits Of Implementing An Encryption Solution In SQL Server?
There are many reasons that you might want to implement an encryption solution in SQL Server, but some of the main benefits are data protection, compliance with regulatory requirements, secure data storage and secure data sharing, and of course, legal protection.
Technical SQL Server Coding Questions
Now, before we wrap up our list of SQL server interview questions, let’s take a look at some technical questions that require you to use your SQL skills to perform some database admin tasks with SQL Server.
51. Write A Sql Query To Retrieve The List Of All Database Names And Their Corresponding File Sizes In A Sql Server Instance.
SELECT name AS DbName, size * 8 / 1024 AS FileSizeMB
WHERE type = 0
52. Write A Sql Query To Identify And Terminate All Active Sessions That Have Been Idle For More Than 30 Minutes In A Sql Server Instance.
DECLARE @IdleMinutes INT = 30;
SELECT session_id, login_time, last_request_start_time
WHERE is_user_process = 1
AND last_request_start_time < DATEADD(MINUTE, -@IdleMinutes, GETDATE())
-- Terminate the identified sessions
-- For example:
-- KILL <session_id>
53. Write A Sql Query To Find The Top 10 Largest Tables By Size In A Specific Database In Sql Server.
SELECT TOP 10
SCHEMA_NAME(schema_id) AS SchemaName,
name AS TableName,
SUM(reserved_page_count) * 8 / 1024 AS TableSizeMB
WHERE index_id < 2
GROUP BY schema_id, name
ORDER BY TableSizeMB DESC;
54. Write A Sql Query To Identify And Kill All Sessions That Are Blocking Other Sessions In A Sql Server Instance.
SELECT session_id AS BlockingSessionID
WHERE blocking_session_id <> 0;
-- Terminate the identified blocking sessions
-- For example:
-- KILL <session_id>
55. Write A Sql Query To Generate A Report Showing The Growth Trend Of A Specific Database's Size Over The Last Month, Including The Total Size, Growth Rate, And Date/Time Of Measurement.
CONVERT(DATE, measurement_time) AS MeasurementDate,
SUM(size) * 8 / 1024 AS TotalSizeMB,
(SUM(size) - LAG(SUM(size)) OVER (ORDER BY measurement_time)) * 8 / 1024 AS GrowthRateMB
FROM sys.dm_io_virtual_file_stats(DB_ID(), NULL)
WHERE file_id = 1 -- Assuming the file_id 1 represents the data file
AND measurement_time >= DATEADD(MONTH, -1, GETDATE())
GROUP BY CONVERT(DATE, measurement_time)
ORDER BY MeasurementDate ASC;
And there you have it, the top 55 SQL server interview questions you need to know in 2024 if you want to feel confident and ready ahead of your next SQL Server interview for database administration.
Whether you’re new to the field or an SQL server pro, we’ve included a range of SQL server interview questions and answers to help you prepare. We’ve also included a series of technical questions on using SQL server for database admin.
By spending the time to review and study these 55 SQL server interview questions and answers, we hope that you will feel more prepared for what to expect during your next SQL server interview.
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