*🔥 Top SQL Interview Questions with Answers*

*🎯 1️⃣ Find 2nd Highest Salary*
📊 Table: employees
id | name | salary
1 | Rahul | 50000
2 | Priya | 70000
3 | Amit | 60000
4 | Neha | 70000

❓ Problem Statement: Find the second highest distinct salary from the employees table.

✅ Solution
SELECT MAX(salary) FROM employees WHERE salary < ( SELECT MAX(salary) FROM employees );

*🎯 2️⃣ Find Nth Highest Salary*
📊 Table: employees
id | name | salary
1 | A | 100
2 | B | 200
3 | C | 300
4 | D | 200

❓ Problem Statement: Write a query to find the 3rd highest salary.

✅ Solution
SELECT salary FROM ( SELECT salary, DENSE_RANK() OVER(ORDER BY salary DESC) r FROM employees ) t WHERE r = 3;

*🎯 3️⃣ Find Duplicate Records*
📊 Table: employees
id | name
1 | Rahul
2 | Amit
3 | Rahul
4 | Neha

❓ Problem Statement: Find all duplicate names in the employees table.

✅ Solution
SELECT name, COUNT(_) FROM employees GROUP BY name HAVING COUNT(_) > 1;

*🎯 4️⃣ Customers with No Orders*
📊 Table: customers
customer_id | name
1 | Rahul
2 | Priya
3 | Amit

📊 Table: orders
order_id | customer_id
101 | 1
102 | 2

❓ Problem Statement: Find customers who have not placed any orders.

✅ Solution
SELECT c.name FROM customers c LEFT JOIN orders o ON c.customer_id = o.customer_id WHERE o.customer_id IS NULL;

*🎯 5️⃣ Top 3 Salaries per Department*
📊 Table: employees
name | department | salary
A | IT | 100
B | IT | 200
C | IT | 150
D | HR | 120
E | HR | 180

❓ Problem Statement: Find the top 3 highest salaries in each department.

✅ Solution
SELECT * FROM ( SELECT name, department, salary, ROW_NUMBER() OVER( PARTITION BY department ORDER BY salary DESC ) r FROM employees ) t WHERE r <= 3;

*🎯 6️⃣ Running Total of Sales*
📊 Table: sales
date | sales
2024-01-01 | 100
2024-01-02 | 200
2024-01-03 | 300

❓ Problem Statement: Calculate the running total of sales by date.

✅ Solution
SELECT date, sales, SUM(sales) OVER(ORDER BY date) AS running_total FROM sales;

*🎯 7️⃣ Employees Above Average Salary*
📊 Table: employees
name | salary
A | 100
B | 200
C | 300

❓ Problem Statement: Find employees earning more than the average salary.

✅ Solution
SELECT name, salary FROM employees WHERE salary > ( SELECT AVG(salary) FROM employees );

*🎯 8️⃣ Department with Highest Total Salary*
📊 Table: employees
name | department | salary
A | IT | 100
B | IT | 200
C | HR | 500

❓ Problem Statement: Find the department with the highest total salary.

✅ Solution
SELECT department, SUM(salary) AS total_salary FROM employees GROUP BY department ORDER BY total_salary DESC LIMIT 1;

*🎯 9️⃣ Customers Who Placed Orders*
📊 Tables: Same as Q4
❓ Problem Statement: Find customers who have placed at least one order.

✅ Solution
SELECT name FROM customers c WHERE EXISTS ( SELECT 1 FROM orders o WHERE c.customer_id = o.customer_id );

*🎯 🔟 Remove Duplicate Records*
📊 Table: employees
id | name
1 | Rahul
2 | Rahul
3 | Amit

❓ Problem Statement: Delete duplicate records but keep one unique record.

✅ Solution
DELETE FROM employees WHERE id NOT IN ( SELECT MIN(id) FROM employees GROUP BY name );

*🚀 Pro Tip:*
👉 In interviews:
First explain logic
Then write query
Then optimize

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*SQL Cheat Sheet for Data Analysts 🗄️📊*

*1. SELECT*
What it is: Used to choose columns from a table
What it does: Returns specific columns of data

Query: Fetch name and salary

SELECT name, salary
FROM employees;

 

*2. FROM*
What it is: Specifies the table
What it does: Tells SQL where to get data from

Query: Fetch all data from employees

SELECT *
FROM employees;

 

*3. WHERE*
What it is: Filters rows based on condition
What it does: Returns only matching rows

Query: Employees with salary > 30000

SELECT *
FROM employees
WHERE salary > 30000;

 

*4. ORDER BY*
What it is: Sorts the data
What it does: Arranges rows in order

Query: Sort by salary (highest first)

SELECT *
FROM employees
ORDER BY salary DESC;

 

*5. COUNT()*
What it is: Counts rows
What it does: Returns total records

Query: Count employees

SELECT COUNT(*)
FROM employees;

 

*6. AVG()*
What it is: Calculates average
What it does: Returns mean value

Query: Average salary

SELECT AVG(salary)
FROM employees;

 

*7. GROUP BY*
What it is: Groups rows by column
What it does: Applies aggregation per group

Query: Avg salary per department

SELECT department, AVG(salary)
FROM employees
GROUP BY department;

 

*8. HAVING*
What it is: Filters grouped data
What it does: Returns filtered groups

Query: Departments with avg salary > 40000

SELECT department, AVG(salary)
FROM employees
GROUP BY department
HAVING AVG(salary) > 40000;

 

*9. INNER JOIN*
What it is: Combines matching rows from tables
What it does: Returns common data

Query: Employees with department names

SELECT e.name, d.department_name
FROM employees e
INNER JOIN departments d
ON e.dept_id = d.dept_id;

 

*10. LEFT JOIN*
What it is: Combines all left + matching right
What it does: Returns all left table data

Query: All employees with departments

SELECT e.name, d.department_name
FROM employees e
LEFT JOIN departments d
ON e.dept_id = d.dept_id;

 

*11. CASE WHEN*
What it is: Conditional logic
What it does: Creates values based on condition

Query: Categorize salary

SELECT name,
CASE
WHEN salary > 40000 THEN 'High'
ELSE 'Low'
END AS category
FROM employees;

 

*12. SUBQUERY*
What it is: Query inside another query
What it does: Uses result of inner query

Query: Salary above average

SELECT name, salary
FROM employees
WHERE salary > (
SELECT AVG(salary)
FROM employees
);

 

*13. RANK()*
What it is: Window function
What it does: Assigns rank without grouping

Query: Rank employees by salary

SELECT name, salary,
RANK() OVER (ORDER BY salary DESC) AS rank
FROM employees;

 

*14. DISTINCT*
What it is: Removes duplicates
What it does: Returns unique values

Query: Unique departments

SELECT DISTINCT department
FROM employees;

 

*15. LIKE*
What it is: Pattern matching
What it does: Filters text patterns

Query: Names starting with A

SELECT *
FROM employees
WHERE name LIKE 'A%';

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💻 *Top Coding Languages for Beginners & Their Uses* 🌟🚀

🔹 *Python* — Easy syntax, great for AI, web, and data
🔹 *JavaScript* — Web interactivity and frontend magic
🔹 *Java* — Enterprise apps and Android development
🔹 *HTML/CSS* — Website structure & styling basics
🔹 *Scratch* — Visual coding for kids & newbies
🔹 *SQL* — Managing and querying databases
🔹 *C#* — Game dev with Unity and Windows apps
🔹 *Ruby* — Simple web app building with Rails
🔹 *Swift* — Making apps for Apple devices
🔹 *PHP* — Server-side scripting for websites

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