1. What is SQL Server?
SQL Server is a relational database management system developed by Microsoft. It allows users to store, retrieve, manipulate, and manage data in a relational database structure.

2. What are the different types of backups in SQL Server?
The different types of backups in SQL Server are Full backup, Differential backup, Transaction log backup, and File or Filegroup backup.

3. What is the difference between CHAR and VARCHAR data types?
CHAR is a fixed-length data type that stores a specific number of characters, while VARCHAR is a variable-length data type that can store up to the maximum defined length.

4. What is a stored procedure?
A stored procedure is a group of SQL statements that are stored in the database and can be executed as a single unit. It helps improve performance and modularity in database applications.

5. What is normalization?
Normalization is the process of organizing data in a database to eliminate redundancy and improve data integrity. It involves splitting a database into multiple tables and defining relationships between them.

6. What is a primary key?
A primary key is a unique identifier for a record in a database table. It ensures that each record in a table is uniquely identifiable and helps enforce data integrity.

7. What is the difference between DELETE and TRUNCATE commands?
The DELETE command is used to remove specific rows from a table, while the TRUNCATE command is used to remove all rows from a table. TRUNCATE is faster but cannot be rolled back.

8. What is an index?
An index is a database structure that improves the speed of data retrieval operations on a database table. It allows the database to find and retrieve specific data more efficiently.

9. What are triggers?
Triggers are special types of stored procedures that are automatically executed in response to specific events or actions in a database. They are used to enforce business rules or perform data validation.

10. What is a view?
A view is a virtual table based on the result of a SQL query. It does not store any data and is used to simplify complex queries, restrict access to data, or provide a different representation of the data.

11. What is the difference between UNION and UNION ALL?
UNION is used to combine the result sets of two or more SELECT statements into a single result set, removing duplicate rows. UNION ALL, on the other hand, combines the result sets without removing duplicates.

12. What is a deadlock?
A deadlock occurs when two or more processes are unable to proceed because each is waiting for the other to release a resource. It can result in a system deadlock where none of the processes can continue.

13. What is the purpose of the COMMIT and ROLLBACK statements?
The COMMIT statement is used to permanently save changes made within a transaction, while the ROLLBACK statement is used to undo all the changes made within a transaction.

14. What are constraints in SQL Server?
Constraints are rules or conditions that are applied to columns or tables to enforce data integrity. Examples include primary key, foreign key, unique, and check constraints.

15. What is the difference between clustered and non-clustered indexes?
A clustered index determines the physical order of data rows in a table, while a non-clustered index is a separate structure that contains a copy of the indexed columns and a pointer to the actual data rows.

16. What is a deadlock?
A deadlock occurs when two or more processes are unable to proceed because each is waiting for the other to release a resource. It can result in a system deadlock where none of the processes can continue.

17. What is the purpose of the COMMIT and ROLLBACK statements?
The COMMIT statement is used to permanently save changes made within a transaction, while the ROLLBACK statement is used to undo all the changes made within a transaction.

18. What are constraints in SQL Server?
Constraints are rules or conditions that are applied to columns or tables to enforce data integrity. Examples include primary key, foreign key, unique, and check constraints.

19. What is the difference between clustered and non-clustered indexes?
A clustered index determines the physical order of data rows in a table, while a non-clustered index is a separate structure that contains a copy of the indexed columns and a pointer to the actual data rows.

20. What is the difference between the HAVING and WHERE clauses?
The WHERE clause is used to filter rows before grouping and aggregation, while the HAVING clause is used to filter groups after grouping and aggregation. The HAVING clause is used in conjunction with the GROUP BY clause.

1. What is SQL Server?
SQL Server is a relational database management system created by Microsoft. It allows you to store, retrieve, and manage data efficiently.

2. What is a Primary Key?
A Primary Key is a unique identifier for a record in a table. It ensures that each record has a unique identity and can be used to enforce data integrity.

3. What is a Foreign Key?
A Foreign Key is a field in a table that refers to the Primary Key of another table. It establishes a relationship between two tables and enforces referential integrity.

4. What is the difference between VARCHAR and CHAR?
VARCHAR is a variable-length character data type that can store up to 8,000 characters. CHAR is a fixed-length character data type that always stores the specified length, padded with spaces if necessary.

5. What is the difference between DELETE and TRUNCATE?
DELETE command is used to remove one or more rows from a table, while TRUNCATE command is used to remove all rows from a table. TRUNCATE is faster as it does not log individual row deletions.

6. What is a Clustered Index?
A Clustered Index determines the physical order of data in a table. Each table can have only one Clustered Index, and it is generally created on the Primary Key.

7. What is a Non-Clustered Index?
A Non-Clustered Index is a separate structure that contains a sorted copy of selected columns from a table. Unlike Clustered Index, a table can have multiple Non-Clustered Indexes.

8. What is the difference between UNION and UNION ALL?
UNION combines the result sets of two or more SELECT statements, removing any duplicate rows. UNION ALL, on the other hand, combines the result sets including duplicate rows.

9. What is the purpose of the GROUP BY clause?
The GROUP BY clause is used to group rows that have the same values in specified columns. It is commonly used in conjunction with aggregate functions to perform calculations on grouped data.

10. What is the purpose of the HAVING clause?
The HAVING clause is used to filter rows in a grouped result set based on a specified condition. It is similar to the WHERE clause but operates on grouped data.

11. What is a Stored Procedure?
A Stored Procedure is a precompiled set of SQL statements that performs a specific database task. It is stored in the database and can be called multiple times with different parameters.

12. What is a Trigger?
A Trigger is a special type of stored procedure that is automatically executed when a specific event (like INSERT, UPDATE, or DELETE) occurs on a table. It is commonly used to maintain data integrity.

13. What is a View?
A View is a virtual table derived from one or more tables or views. It allows you to retrieve data from multiple tables as if it were a single table, simplifying complex queries.

14. What is the difference between a View and a Table?
A Table contains the actual data, while a View is a virtual table that does not store any data. Views are based on one or more tables and provide a customized perspective on the data.

15. What is the purpose of the COMMIT statement?
The COMMIT statement is used to permanently save the changes made within a transaction to the database. It ensures data consistency and durability.

16. What is the purpose of the ROLLBACK statement?
The ROLLBACK statement is used to undo changes made within a transaction. It allows reverting to the state before the transaction began.

17. What is a deadlock?
A deadlock occurs when two or more transactions permanently block each other from proceeding, resulting in a state where none of the transactions can progress. It requires intervention to resolve.

18. What is the purpose of the INDEX command in SQL Server?
The INDEX command is used to create an index on a table or a view. Indexes improve performance by enabling faster data retrieval and optimizing query execution.

19. What is the difference between INNER JOIN and OUTER JOIN?
INNER JOIN returns only the matching rows between two tables based on the common column(s). OUTER JOIN returns all rows from one table and only the matching rows from the other table.

20. What are the different types of backups in SQL Server?
The different types of backups in SQL Server are Full Backup, Differential Backup, and Transaction Log Backup. Full Backup includes all data and objects, Differential Backup includes only changed data since the last Full Backup, and Transaction Log Backup includes log records for point-in-time recovery.

1. What is a clustered index?
A clustered index is a type of index that determines the physical order of data in a table. It is created on a table’s primary key by default, but can also be created on any other column. Each table can have only one clustered index.

2. What is the difference between a clustered and a non-clustered index?
A clustered index determines the physical order of data in a table, while a non-clustered index does not. A table can have only one clustered index, but multiple non-clustered indexes.

3. Define recursive CTE (Common Table Expression).
A recursive CTE is a CTE that references itself in its own definition. It allows querying hierarchical or self-referencing data structures.

4. What are the ACID properties in database transactions?
ACID stands for Atomicity, Consistency, Isolation, and Durability. These properties ensure that database transactions are reliable and maintain data integrity.

5. What is the difference between UNION and UNION ALL in SQL?
UNION combines the result sets of two or more SELECT statements, removing duplicate rows, while UNION ALL combines the result sets without removing duplicates.

6. What is a self-join?
A self-join is a join operation where a table is joined with itself. It is useful when working with hierarchical data or when referencing a table multiple times in a single SQL query.

7. What is a scalar function in SQL Server?
A scalar function is a user-defined function that returns a single value. It can be used in expressions and SELECT statements.

8. What are triggers in SQL Server?
Triggers are special types of stored procedures that are automatically executed in response to specific database events, such as data changes or table modifications.

9. What is the purpose of the COALESCE function in SQL?
The COALESCE function is used to return the first non-null value from a list of expressions. It is often used to replace NULL values with alternative values.

10. What are the different isolation levels in SQL Server?
The different isolation levels in SQL Server are READ UNCOMMITTED, READ COMMITTED, REPEATABLE READ, and SERIALIZABLE. These levels determine how transactions interact with each other and control concurrent access to data.

11. What is dynamic SQL? Provide an example.
Dynamic SQL is a programming technique that allows SQL statements to be constructed and executed dynamically at runtime. An example is:
“`sql
DECLARE @sqlQuery NVARCHAR(MAX)
SET @sqlQuery = ‘SELECT * FROM TableName WHERE Column = ”Value”’
EXECUTE sp_executesql @sqlQuery
“`

12. Explain the purpose of the PIVOT and UNPIVOT operators in SQL Server.
The PIVOT operator is used to rotate rows into columns, creating a cross-tabular result set. The UNPIVOT operator performs the opposite operation, transforming columns into rows.

13. What is the purpose of the MERGE statement in SQL Server?
The MERGE statement is used to perform insert, update, or delete operations in a single statement based on the results of a join. It simplifies the handling of data synchronization and changes.

14. What is the purpose of the TRY-CATCH block in SQL Server?
The TRY-CATCH block is used for error handling in SQL Server. It allows catching and handling exceptions within a defined scope, ensuring graceful error handling and preventing the termination of the entire script.

15. How does the deadlock occur in SQL Server?
A deadlock occurs when two or more processes or transactions are waiting for each other to release resources, resulting in a deadlock situation where none of them can proceed. SQL Server automatically detects and resolves deadlocks.

16. What is the purpose of the ROW_NUMBER() function in SQL Server?
The ROW_NUMBER() function is used to assign a unique sequential number to each row in the result set. It is frequently used for pagination or ranking purposes.

17. Explain the concept of database normalization.
Database normalization is the process of organizing data in a database design to minimize redundancy and dependency. It involves breaking down a large table into smaller tables and defining relationships between them.

18. What is an execution plan in SQL Server?
An execution plan is a detailed blueprint of how SQL Server executes a query. It shows the order of operations, the use of indexes, and the estimated cost of each step.

19. What is the purpose of the NOLOCK hint in SQL Server?
The NOLOCK hint allows reading uncommitted data, also known as a “dirty read.” It can improve query performance in certain scenarios but may return inconsistent or incorrect data.

20. What are database transactions and why are they important?
A database transaction is a sequence of operations that are treated as a single unit of work. Transactions ensure data consistency and integrity by allowing a group of operations to be either fully completed or rolled back if an error occurs.