SQL Interview Questions

SQL, which stands for Structured Query Language, is a standardized programming language specifically designed for managing and manipulating relational databases. SQL is used to perform various operations on the data stored in databases, such as querying, updating, inserting, and deleting records.

Key Functions of SQL

1. Data Querying:

   • SELECT: Retrieve data from one or more tables.

     SELECT * FROM employees;

   • WHERE: Filter records based on specific conditions.

     SELECT * FROM employees WHERE department = 'Sales';

2. Data Manipulation:

   • INSERT: Add new records to a table.

     INSERT INTO employees (name, department, salary) VALUES ('John Doe', 'Sales', 50000);

   • UPDATE: Modify existing records.

     UPDATE employees SET salary = 55000 WHERE name = 'John Doe';

   • DELETE: Remove records from a table.

     DELETE FROM employees WHERE name = 'John Doe';

3. Data Definition:

   • CREATE: Create new tables or databases.

     CREATE TABLE employees (id INT PRIMARY KEY, name VARCHAR(50), department VARCHAR(50), salary INT);

   • ALTER: Modify the structure of an existing table.

     ALTER TABLE employees ADD COLUMN hire_date DATE;

   • DROP: Delete tables or databases.

     DROP TABLE employees;

4. Data Control:

   • GRANT: Provide users with specific permissions.

     GRANT SELECT ON employees TO user_name;

   • REVOKE: Remove users' permissions.

     REVOKE SELECT ON employees FROM user_name;

Benefits of SQL

1. Standardization:

   • SQL is a standardized language (ANSI and ISO standards), which means it is widely recognized and used across various relational database management systems (RDBMS) such as MySQL, PostgreSQL, Oracle, and SQL Server.

2. Powerful and Flexible:

   • SQL provides powerful capabilities for complex queries, data manipulation, and database management, making it a versatile tool for various database operations.

3. Declarative Nature:

   • SQL is a declarative language, meaning that it allows users to specify what they want to do without detailing how to do it. This simplifies data interaction and reduces the need for procedural code.

4. Integration with Other Languages:

   • SQL can be integrated with other programming languages like Python, Java, and C#, allowing for the development of robust and dynamic applications that interact with databases.

Conclusion

SQL is a crucial language for anyone working with relational databases, offering a comprehensive set of tools for data querying, manipulation, definition, and control. Its standardization, power, flexibility, and ease of integration make it an indispensable skill in the field of data management and application development.