17/Apr/2021 | 10 minutes to read
Here is a List of essential SQL Server Interview Questions and Answers for Freshers and mid level of Experienced Professionals. All answers for these SQL Server questions are explained in a simple and easiest way. These questions will help you to clear your next Job interview.
These interview questions are targeted for a SQL Server. You must know the answers of these frequently asked SQL Server questions to clear your next Job interview.
1. What are the ACID properties? Or list and explain each of the ACID properties that collectively guarantee that database transactions are processed reliably.
ACID (A - Atomicity, C - Consistency, I - Isolation, D - Durability) is a set of properties that guarantee that database transactions are processed reliably. They are defined as follows:
2. What is UNION in SQL Server? What is the difference between UNION and UNION ALL?
UNION it merges the contents of two tables which are structurally compatible into a single combined table.
The difference between UNION and UNION ALL is that UNION will omit duplicate records whereas UNION ALL will include duplicate records.
It is important to note that the performance of UNION ALL will typically be better than UNION, since UNION requires the server to do the additional work of removing any duplicates. So, in the cases where it is certain that there will not be any duplicates, or where having duplicates is not a problem, use of UNION ALL would be recommended for better performance.
3. What is the difference between the WHERE and HAVING clauses? What is Group by clause?
Select * from Employee Where Id > 10;
Select Name, Salary from Employee Group by Name, Salary Having SUM(Salary) > 10000;
Select col1, col2, from table group by col1, col2
4. What is Index? Define Clustered and Non-Clustered index.
Index Index is an on disk structure associated with table or view that is built from one or more columns in table or view. An Index speeds the retrieval of data from table or view.
Index contains key built from one or more column(s). These keys are stored in the form of B-tree data structure that enables the SQL Server to find the rows associated with these
keys in a quick and efficient way.
For more visit Index in SQL Server
In SQL Server there are 2 types of Indexes.
5. How to delete Duplicate Records in SQL Server?
We can use CTE, Row_Number() with over clause.
id - is column by which u find duplicates OR you can also use below code if table has identity column to identify duplicate data.
With CTE AS ( select *,RN = ROW_NUMBER() over(partition by id Order by id) from Employee1 ) delete from CTE where RN>1;
DELETE FROM MyTable WHERE ID NOT IN ( SELECT MAX(ID) FROM MyTable GROUP BY DuplicateColumn1, DuplicateColumn2, DuplicateColumn3)
6. Explain Row_Number, RANK and DENSE_Rank in SQL Server.
ROW_NUMBER, RANK, DENSE_RANK can be used with partition or without it but not without over clause.
USE [Practice] GO /****** Object: Table [dbo].[Employee] Script Date: 31-05-2019 10:50:47 ******/ SET ANSI_NULLS ON GO SET QUOTED_IDENTIFIER ON GO CREATE TABLE [dbo].[Employee] ( [Id] INT NOT NULL, [Name] VARCHAR (50) NULL, [Salary] VARCHAR (50) NULL ); INSERT INTO [dbo].[Employee] ([Id], [Name], [Salary]) VALUES (1, N'bhanu',N'100') INSERT INTO [dbo].[Employee] ([Id], [Name], [Salary]) VALUES (2, N'bhanu',N'200') INSERT INTO [dbo].[Employee] ([Id], [Name], [Salary]) VALUES (3, N'Faizan',N'200') INSERT INTO [dbo].[Employee] ([Id], [Name], [Salary]) VALUES (4, N'Faizan',N'200') INSERT INTO [dbo].[Employee] ([Id], [Name], [Salary]) VALUES (5, N'Kap', N'300') INSERT INTO [dbo].[Employee] ([Id], [Name], [Salary]) VALUES (6, N'Jap', N'100') INSERT INTO [dbo].[Employee] ([Id], [Name], [Salary]) VALUES (7, N'Abhi', N'500') INSERT INTO [dbo].[Employee] ([Id], [Name], [Salary]) VALUES (8, N'Shan', N'200') ;with CTE AS(select *, ROW_NUMBER() over(partition by Name,Salary order by Id) asRN from Employee) select * from CTE --select * from CTE where RN>1 -- here you can delete duplicate records where RN>1 -- delete from CTE where RN>1 select *, ROW_NUMBER() over(order by Id) as RN from Employee select *, ROW_NUMBER() over(partition by Name,Salary order by Id) as RN fromEmployee select *, RANK() over(order by Name) as rn from Employee select *, RANK() over(partition by Name order by Name) as rn from Employee select *, Dense_RANK() over(order by Name) as rn from Employee select *, Dense_RANK() over(partition by Salary order by Name) as rn fromEmployee -- find nth highest salary - always use dense rank as rank will skip some numbers. -- so it will not give any result for those skipped numbers select * from Employee ;with CTE1 as (select *, RANK() over (order by salary desc) as RN from Employee) select top 1 * from CTE1 where RN=4 -- 4th Highest from highest to lowest select * from Employee ;with CTE1 as (select *, DENSE_RANK() over (order by salary desc) as RN fromEmployee) select top 1 * from CTE1 where RN=2 -- 2nd highest from
7. How to select top nth Records?
Let's take the example to select top 5th record from down
select top 1 id from (select top 5 id from employee1 order by id desc)sub order by id asc
8. Write self join query with following table structure.
Table select query is
SELECT [id],[ename],[managerId] FROM [Practic].[dbo].[employee1] // Self Join Example: we will fetch emp name and manager name from same table using self join. select e.ename, m.ename from employee1 e inner join employee1 m on e.managerId = m.id
9. What is SQL Server Profiler?
SQL Profiler is an graphical user interface (GUI) tool that is used for tracing, recreating and troubleshooting the problems in SQL Server. It's used to identify slow executing queries and production problems by capturing the events. For example, you can monitor a production environment to see which stored procedures are affecting performance by executing too slowly. Fore more visit SQL Server Profiler. SQL Profiler is used for following type of activities.
10. Write a query to select all the Even and Odd number records from a table.
To select all even number records:
To select all odd number records:
SELECT * FROM TABLE WHERE ID % 2 = 0
Select * from table where id % 2 != 0
11. Why stored procedures are fast as compare to run query by c#?
Stored procedures are fast because these are in compile form means no need to compile when we run it. Whenever we run some query by c# (ORM or ado.net) then first query get compiled then create execution plan but in case of store procedures execution plan does not get created again as it's already created when we write store procedures.
12. What is Self Join and why is it required?
Self Join provide the capability of joining one table with itself. for example, you have one table 'employee' with three columns id, name, manager_id. Now you want to print the name of employee and his manager in same row.
SELECT e.name EMPLOYEE, m.name MANAGER FROM EMPLOYEE e, EMPLOYEE m WHERE e.manager_id = m.id
13. What is the difference between Truncate, Delete and Drop commands?
All these are the SQL commands used on the basis of different needs as below.
14. How can you improve Stored Procedure Performance?
You should focus on certain points for your Stored Procedure performance as below.
15. How to concatenate text from multiple rows into a single text string in SQL server? Consider below rows.
Test-1 Test-2 Test-3 Expected O/p from above 3 rows should be - Test1, Test2, Test3
16. How to convert rows to columns in SQL Server?
17. How to UPDATE from a SELECT in SQL Server?
18. How to insert the result of a stored procedure into temporary table?
19. How to split a comma-separated value to columns in SQL Server?
20. How to check Query Execution Plan in SQL Server?
21. What is the difference between
22. How to escape a single quote in SQL Server?
23. What is the difference between
NOT IN vs
24. How to return only the Date from a DateTime datatype in SQL Server?
1. How much will you rate your self in SQL Server?
When you attend an interview, Interviewer may ask you to rate your self in specific Technology like SQL Server, So It's depend on your knowledge and work experience in SQL Server.
2. What challenges did you face while working on SQL Server?
This question may be specific to your technology and completely depends on your past work experience. So you need to just explain the challenges you faced related to SQL Server in your Project.
3. What was your role in last Project related to SQL Server?
It's based on your role and responsibilities assigned to you and what functionality you implemented using SQL Server in your project. This question is generally asked in every interview.
4. How much experience do you have in SQL Server?
Here you can tell about your overall work experience on SQL Server.
5. Have you done any SQL Server Certification or Training?
It's depend on candidate like you have done any SQL Server training or certification. Certifications or trainings are not essential but good to have.
We have covered some frequently asked SQL Server Interview Questions and Answers to help you for your Interview. All these Essential SQL Server Interview Questions are targeted for mid level of experienced Professionals and freshers.
While attending any SQL Server Interview if you face any difficulty to answer any question please write to us at email@example.com. Our IT Expert team will find the best answer and will update on portal. In case if we find any new SQL Server questions, we will update the same here.