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Microsoft SQL Interview Questions and Answers
Question 1:
What is Microsoft SQL Server?
Microsoft SQL Server is a relational database management system (RDBMS) developed by Microsoft. It provides a robust and scalable platform for storing, managing, and retrieving data. SQL Server supports a wide range of database-related functionalities, including data storage, data manipulation, data analysis, and business intelligence.
Question 2:
What are the different editions of Microsoft SQL Server?
Microsoft SQL Server is available in several editions, including:
- Enterprise Edition: Provides comprehensive data management and business intelligence capabilities.
- Standard Edition: Offers basic database management functionalities.
- Express Edition: A free, lightweight edition suitable for small-scale applications.
- Developer Edition: Similar to the Enterprise Edition but licensed for development and testing purposes.
- Web Edition: Designed for hosting websites and web applications.
Question 3:
What is the difference between CHAR and VARCHAR data types in SQL Server?
In SQL Server, the CHAR and VARCHAR data types are used for storing character data.
- CHAR: It is a fixed-length data type that stores a fixed number of characters. If the actual value is shorter than the defined length, it is padded with spaces.
- VARCHAR: It is a variable-length data type that stores a variable number of characters. It only uses the required amount of storage for the actual value.
Question 4:
What is a primary key in SQL Server?
A primary key is a column or a combination of columns that uniquely identifies each row in a table. It enforces data integrity and ensures that there are no duplicate or null values in the primary key column(s). In SQL Server, a primary key is created using the PRIMARY KEY constraint.
Question 5:
What is the difference between DELETE and TRUNCATE in SQL Server?
- DELETE: It is a DML (Data Manipulation Language) statement used to remove specific rows from a table based on a condition. DELETE can be rolled back and also triggers associated triggers.
- TRUNCATE: It is a DDL (Data Definition Language) statement used to remove all rows from a table. TRUNCATE cannot be rolled back, and it does not trigger associated triggers. It is faster than DELETE as it does not log individual row deletions.
Question 6:
What are stored procedures in SQL Server?
A stored procedure is a named set of SQL statements that are precompiled and stored in the database. They can be called and executed multiple times with different parameters. Stored procedures help improve performance by reducing network traffic and improving code reusability and security. They can also encapsulate complex logic and provide an additional layer of abstraction between the application and the database.
Question 7:
What is the purpose of indexes in SQL Server?
Indexes in SQL Server are used to improve the performance of database queries by allowing faster data retrieval. They are created on one or more columns of a table and provide a quick way to look up data based on the values in those columns. Indexes can speed up SELECT, UPDATE, and DELETE operations but may slightly slow down data modification operations (INSERT, UPDATE, DELETE) as they require additional maintenance.
Question 8:
What is a foreign key in SQL Server?
A foreign key is a column or a set of columns in a table that references the primary key of another table. It establishes a relationship between two tables, enforcing referential integrity. The foreign key ensures that the values in the referencing column(s) match the values in the referenced column(s) or are null. Foreign keys can be used to create joins between related tables and maintain data consistency across the database.
Question 9:
What is normalization in the context of database design?
Normalization is a technique used in database design to eliminate data redundancy and improve data integrity. It involves dividing a database into multiple related tables and defining relationships between them. The goal of normalization is to reduce data duplication and ensure that each piece of data is stored in only one place. Normalization follows a set of rules (normal forms) to structure the data efficiently and avoid anomalies.
Question 10:
What is the difference between UNION and UNION ALL in SQL Server?
- UNION: It is an operator used to combine the result sets of two or more SELECT statements into a single result set. UNION removes duplicate rows from the result set.
- UNION ALL: It is also an operator used to combine the result sets of two or more SELECT statements. However, UNION ALL does not remove duplicate rows and includes all rows from all the SELECT statements.
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