SQL

What is SQL?

SQL (Structured Query Language) is a domain-specific programming language used for managing and manipulating relational databases. It is the standard language for interacting with databases to perform tasks such as retrieving, inserting, updating, and deleting data. SQL allows users to create and manage database structures, define relationships between tables, and query data using a series of commands.

Key Components:

• Tables: Data is organized in rows and columns.
• Columns: Define the structure of the table (e.g., id, name, salary).
• Rows: Represent individual records in a table.
• Primary Key: A unique identifier for each record.
• Foreign Key: Establishes relationships between table

With questions i perform my queries and solves the problem statements:

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First : I Create a database

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Second: I create three tables

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Third : I insert a data into the Department table

Output

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Fourth: I insert a data into the Employee table

Output

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Fifth : I insert a data into project_assigment table

Ouput

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sixth : I practice questions taking these tables and solve them:

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Question 1. Find the Second Highest Salary

Problem: Find the second highest salary from the Employee table.

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2. List Departments with More Than 3 Employees

Problem: List department names where the number of employees is greater than 3.

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3.. Retrieve the Top 3 Highest-Paid Employees in Each Department

Problem: List the top 3 highest-paid employees from each department.

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4. Fetch the second-highest salary from the employees table.

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5.Retrieve names of employees whose names start with "J" and end with "N".

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6. Display the total count of employees grouped by their department.

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7.Find employees who have never been assigned a project id .

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8. Find the maximum, minimum, and average salary of employees in each department.

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9. Fetch names of employees who earn more than the average salary in their department.

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10. Find names of employees who work in the same department as "John Doe".

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11. Find departments with more than 5 employees.

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12.Fetch employees with salaries in the top 10%.

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13.Retrieve the list of duplicate records in a table.

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14. Write a query to find employees with the same salary.

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15. Calculate the running total of salaries.

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16. Find the rank of employees based on their salary within each department.

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17.Fetch the department with the highest average salary.

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18. Find employees whose salary is greater than the department average.

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19. Rank employees by salary within each department.

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20.Find the percentage contribution of each employee's salary within their department.