Interview Questions on Introduction to SQL Server | SQL Server

If you’re preparing for an SQL Server interview, it’s essential to be familiar with foundational concepts like RDBMS, SQL Server installation, databases, tables, and schemas. Here’s a list of 30 interview questions, organized by topics, to help you ace your SQL Server interview.

Section 1: Freshers (Chapters 1-5)

1. Introduction to SQL Server

1. What is SQL Server?
   • SQL Server is a relational database management system (RDBMS) developed by Microsoft to store, manage, and retrieve data. It uses SQL (Structured Query Language) for data manipulation.
2. Explain the different editions of SQL Server.
   • SQL Server offers multiple editions, including Enterprise, Standard, Web, and Express, each designed for different workloads, with varying features and scalability.
3. What is the role of a SQL Server Database Engine?
   • The SQL Server Database Engine is responsible for storing, processing, and securing data, and it includes components for query processing, transaction management, and security enforcement.
4. What is SQL Server Management Studio (SSMS)?
   • SSMS is a tool used for managing SQL Server databases. It provides a graphical interface for interacting with SQL Server, executing queries, and managing database objects.
5. What are the types of backups in SQL Server?
   • SQL Server supports several types of backups: full backup, differential backup, transaction log backup, and file or filegroup backups, each serving a different purpose in data recovery.

2. Basics of RDBMS

6. What is an RDBMS?
   • An RDBMS (Relational Database Management System) is a system that stores data in tables, and ensures data integrity, consistency, and relationship through SQL.
7. What is a primary key in a database?
   • A primary key is a unique identifier for records in a table, ensuring that no two rows have the same key value. It also enforces entity integrity.
8. What is a foreign key in SQL Server?
   • A foreign key is a column or a set of columns in one table that references the primary key in another table, establishing a relationship between the tables.
9. What are normal forms in RDBMS?
   • Normalization is a process of organizing data to minimize redundancy and dependency. Common normal forms include 1NF, 2NF, 3NF, and BCNF.
10. Explain the concept of referential integrity.
    • Referential integrity ensures that relationships between tables remain consistent, meaning that foreign keys always point to valid records in the referenced table.

3. SQL Server Installation and Components

11. What are the components of SQL Server?
    • SQL Server consists of various components, including the Database Engine, SQL Server Management Studio (SSMS), SQL Server Agent, Reporting Services (SSRS), Integration Services (SSIS), and Analysis Services (SSAS).
12. What is the difference between a clustered and non-clustered index in SQL Server?
    • A clustered index determines the physical order of data in a table, whereas a non-clustered index creates a separate structure for faster retrieval of data without altering the table’s order.
13. How do you install SQL Server?
    • To install SQL Server, download the installer from the Microsoft website, follow the setup wizard, select components, configure instance settings, and complete the installation process.
14. What is SQL Server instance?
    • A SQL Server instance is a copy of SQL Server running on a system. Each instance operates independently with its own system databases, configuration settings, and security.
15. What is the purpose of SQL Server Agent?
    • SQL Server Agent is used to automate administrative tasks, such as running scheduled jobs, maintaining databases, and managing backups.

4. Understanding Databases, Tables, and Schemas

16. What is a database in SQL Server?
    • A database in SQL Server is a structured collection of data that is stored and managed by SQL Server, including tables, indexes, views, and stored procedures.
17. What is a schema in SQL Server?
    • A schema is a container for database objects such as tables, views, and procedures. It helps organize and secure data by grouping objects logically.
18. What is a table in SQL Server?
    • A table in SQL Server is a collection of rows and columns that store data. Each table has a specific structure defined by its columns and data types.
19. What are system databases in SQL Server?
    • System databases in SQL Server include master, model, msdb, and tempdb. These databases are essential for SQL Server’s operation and management.
20. How do you create a table in SQL Server?
    • You can create a table in SQL Server using the CREATE TABLE statement, specifying column names, data types, and constraints.

5. Basic Data Types and Constraints

21. What are the common data types in SQL Server?
    • Common SQL Server data types include INT, VARCHAR, DATE, DATETIME, FLOAT, and BOOLEAN. These data types define the kind of data that can be stored in a column.
22. What is the difference between CHAR and VARCHAR data types?
    • CHAR is a fixed-length data type, while VARCHAR is variable-length. CHAR uses the exact number of bytes specified, while VARCHAR only uses as much space as needed.
23. What is a default constraint in SQL Server?
    • A default constraint provides a default value for a column when no value is specified during an insert operation.
24. What is a unique constraint?
    • A unique constraint ensures that all values in a column or a set of columns are distinct, preventing duplicate entries.
25. Explain the concept of a check constraint.
    • A check constraint limits the range of values that can be entered into a column, ensuring data integrity by enforcing a condition on the values.

6. Querying Databases

26. What is the SELECT statement in SQL Server?
    • The SELECT statement is used to query data from one or more tables. It allows retrieving specific columns, filtering results, and sorting them.
27. What is the difference between INNER JOIN and OUTER JOIN?
    • An INNER JOIN returns only the rows with matching values in both tables, whereas an OUTER JOIN returns all rows from one table and matching rows from the other table, filling non-matching rows with NULL.
28. What is the use of the GROUP BY clause in SQL Server?
    • The GROUP BY clause is used to aggregate data, such as calculating sums or averages, based on a specific column or set of columns.
29. What is the HAVING clause used for?
    • The HAVING clause is used to filter records after an aggregate function, unlike the WHERE clause, which filters records before aggregation.
30. What are subqueries in SQL Server?
    • A subquery is a query within another query. It can return a single value, a list of values, or a table to be used in the outer query.