SQL Interview Questions & Answers

Q: Fetch all orders where the total_value is greater than the average order value.?

Input Table: Orders order_id customer_id total_value 901 1 5000 902 2 7000 903 3 6000 904 4 8000 I use a subquery to calculate the average order value using AVG() . Then I use the result in the outer query to return orders whose total value is greater than that average.

Q: Find the most frequently sold product in each category.?

Products product_id category product_name 601 A Apple 602 A Banana 603 B Milk 604 B Bread Sales sale_id product_id quantity 1 601 10 2 602 5 3 601 8 4 603 12 5 604 4 Then we can calculate total quantity sold: Therefore: SQL concept The solution normally involves:

Q: Calculate the average sales amount for each region.

Input Table: Sales sales_id region sales_amount 501 North 50000 502 South 70000 503 North 80000 504 West 90000 I group the sales records by region using GROUP BY , and then use the AVG() aggregate function to calculate the average sales amount for each region.

Q: Write a query to retrieve the first and last purchase date for each customer.?

Input Table: Transactions transaction_id customer_id purchase_date 301 1 2024-01-10 302 2 2024-01-12 303 1 2024-02-15 304 2 2024-02-20 305 1 2024-03-05

Q: Find customers who have placed more than 5 orders in the last 30 days.?

Input Table: Orders order_id customer_id order_date 201 1 2024-02-15 202 2 2024-02-10 203 1 2024-02-18 204 3 2024-02-20 205 1 2024-02-25 206 2 2024-02-27 207 1 2024-03-02

Q: Write a query to fetch the top 3 employees with the highest salaries from an Employees table.?(Asked in Accenture)

Fetch the Top 3 Employees with the Highest Salaries Input Table: Employees emp_id emp_name salary 101 Alice 95000 102 Bob 87000 103 Charlie 91000 104 David 75000 105 Eve 99000

pyspark·

4d agoInterview Question

Q.1

SQL Interview Question: A Query Taking 2 Minutes Now Takes 20 Minutes. What Will You Do?

Medium

"I wouldn't immediately rewrite the query. First, I would investigate the root cause step by step.

Check system performance: Verify CPU, memory, disk I/O, and database load.
Check execution plan: Compare the current execution plan with the previous one to identify performance changes.
Check data volume: See whether the number of records has increased significantly.
Check indexes: Verify whether the query is using indexes or performing unnecessary full table scans.
Check joins: Identify inefficient joins or unexpected increases in matching records.
Check partition pruning: Ensure the query reads only the required partitions instead of scanning historical data.
Check statistics: Verify that database statistics are updated so the optimizer can choose an efficient plan.
Check recent changes: Investigate recent deployments, query modifications, or infrastructure changes.

Finally, after identifying the root cause, I would apply the appropriate optimization, test it safely, and monitor execution time to confirm the improvement."

Vishal Taneja·

Sep 19, 2026Interview Question

Q.2

Fetch all orders where the total_value is greater than the average order value.?

Medium

Input Table: `Orders`

order_id	customer_id	total_value
901	1	5000
902	2	7000
903	3	6000
904	4	8000

I use a subquery to calculate the average order value using AVG(). Then I use the result in the outer query to return orders whose total value is greater than that average.

-- =========================================
-- QUESTION 10
-- Find Orders Where Total Order Value
-- Exceeds the Average Order Value
-- =========================================
 
-- =========================================
-- 1. Remove Existing Table
-- =========================================
 
DROP TABLE IF EXISTS Orders;
 
-- =========================================
-- 2. Create Orders Table
-- =========================================
 
CREATE TABLE Orders (
    order_id INT,
    customer_id INT,
    total_value DECIMAL(10, 2)
);
 
-- =========================================
-- 3. Insert Orders
-- =========================================
 
INSERT INTO Orders (
    order_id,
    customer_id,
    total_value
)
VALUES
    (901, 1, 5000),
    (902, 2, 7000),
    (903, 3, 6000),
    (904, 4, 8000);
 
-- =========================================
-- 4. Select All Orders
-- =========================================
 
SELECT *
FROM Orders;
 
-- =========================================
-- 5. Calculate Average Order Value
-- =========================================
 
SELECT
    AVG(total_value) AS average_order_value
FROM Orders;
 
-- =========================================
-- 6. Find Orders Above Average
-- =========================================
 
SELECT
    order_id,
    customer_id,
    total_value
FROM Orders
WHERE total_value &gt; (
    SELECT AVG(total_value)
    FROM Orders
);
▶ Run to see output

Vishal Taneja·

Sep 19, 2026Interview Question

Q.3

Find the most frequently sold product in each category.?

Medium

Products

product_id	category	product_name
601	A	Apple
602	A	Banana
603	B	Milk
604	B	Bread

Sales

sale_id	product_id	quantity
1	601	10
2	602	5
3	601	8
4	603	12
5	604	4

Then we can calculate total quantity sold:


Apple  → 10 + 8 = 18
Banana → 5
Milk   → 12
Bread  → 4

Therefore:


Category A → Apple
Category B → Milk

SQL concept

The solution normally involves:


Products
   ↓
JOIN Sales
   ↓
GROUP BY category + product
   ↓
SUM(quantity) / COUNT(*)
   ↓
Rank products within each category
   ↓
Take rank = 1

-- =========================================
-- QUESTION 8
-- Find the Most Frequently Sold Product
-- in Each Category
-- =========================================
 
-- =========================================
-- 1. Remove old tables if they exist
-- =========================================
 
DROP TABLE IF EXISTS ProductSales;
DROP TABLE IF EXISTS Products;
 
-- =========================================
-- 2. Create Products Table
-- =========================================
 
CREATE TABLE Products (
    product_id INT,
    category VARCHAR(50),
    product_name VARCHAR(100)
);
 
-- =========================================
-- 3. Insert Products
-- =========================================
 
INSERT INTO Products (
    product_id,
    category,
    product_name
)
VALUES
    (601, 'A', 'Apple'),
    (602, 'A', 'Banana'),
    (603, 'A', 'Mango'),
    (604, 'B', 'Milk'),
    (605, 'B', 'Bread'),
    (606, 'B', 'Butter');
 
-- =========================================
-- 4. Create ProductSales Table
-- =========================================
 
CREATE TABLE ProductSales (
    sale_id INT,
    product_id INT
);
 
-- =========================================
-- 5. Insert Sales
-- =========================================
 
INSERT INTO ProductSales (
    sale_id,
    product_id
)
VALUES
    (1, 601),
    (2, 601),
    (3, 601),
    (4, 602),
    (5, 602),
    (6, 603),
    (7, 604),
    (8, 604),
    (9, 604),
    (10, 604),
    (11, 605),
    (12, 605),
    (13, 606);
 
-- =========================================
-- 6. Check Products
-- =========================================
 
SELECT *
FROM Products;
 
-- =========================================
-- 7. Check Product Sales
-- =========================================
 
SELECT *
FROM ProductSales;
 
-- =========================================
-- 8. Count How Many Times Each Product
--    Was Sold
-- =========================================
 
SELECT
    p.category,
    p.product_id,
    p.product_name,
    COUNT(ps.sale_id) AS times_sold
FROM Products p
JOIN ProductSales ps
    ON p.product_id = ps.product_id
GROUP BY
    p.category,
    p.product_id,
    p.product_name
ORDER BY
    p.category,
    times_sold DESC;
 
-- =========================================
-- 9. Find Most Frequently Sold Product
--    in Each Category
-- =========================================
 
WITH product_sales AS (
    SELECT
        p.category,
        p.product_id,
        p.product_name,
        COUNT(ps.sale_id) AS times_sold
    FROM Products p
    JOIN ProductSales ps
        ON p.product_id = ps.product_id
    GROUP BY
        p.category,
        p.product_id,
        p.product_name
),
 
ranked_products AS (
    SELECT
        category,
        product_id,
        product_name,
        times_sold,
        ROW_NUMBER() OVER (
            PARTITION BY category
            ORDER BY times_sold DESC
        ) AS rn
    FROM product_sales
)
 
SELECT
    category,
    product_id,
    product_name,
    times_sold
FROM ranked_products
WHERE rn = 1
ORDER BY category;
▶ Run to see output

pyspark·

Sep 19, 2026Interview Question

Q.4

Find customers who have never placed an order.?

Medium

The key concept here is a LEFT JOIN with IS NULL.

1. Customers Table

customer_id	customer_name
1	John
2	Alice
3	Bob

2. Orders Table

order_id	customer_id
101	1
102	2

I use a LEFT JOIN between Customers and Orders on customer_id. The LEFT JOIN keeps all customers, including those without orders. Then I filter where the Orders customer_id is NULL to identify customers who have never placed an order.

CREATE TABLE Customers (
    customer_id INT,
    customer_name VARCHAR(100)
);
INSERT INTO Customers (customer_id, customer_name)
VALUES
    (1, 'John'),
    (2, 'Alice'),
 
    (3, 'Bob');
CREATE TABLE Orders (
    order_id INT,
    customer_id INT
 
);
INSERT INTO Orders (order_id, customer_id)
VALUES
    (101, 1),
 
    (102, 2);
 
SELECT
    c.customer_id,
    c.customer_name
FROM Customers c
LEFT JOIN Orders o
    ON c.customer_id = o.customer_id
 
WHERE o.customer_id IS NULL;
▶ Run to see output

pyspark·

Sep 19, 2026Interview Question

Q.5

Find the second-highest salary from the Employees table without using LIMIT or TOP.

Medium

Example Employees Table

Suppose we have:

emp_id	emp_name	salary
101	Alice	95000
102	Bob	87000
103	Charlie	91000
104	David	75000
105	Eve	99000

I use a subquery to find the maximum salary, filter out that salary using the WHERE clause, and then use MAX() on the remaining salaries to get the second-highest salary.

CREATE TABLE Employees (
    emp_id INT,
    emp_name VARCHAR(100),
    salary DECIMAL(10, 2)
);
INSERT INTO Employees (emp_id, emp_name, salary)
VALUES
    (101, 'Alice', 95000),
    (102, 'Bob', 87000),
    (103, 'Charlie', 91000),
    (104, 'David', 75000),
 
    (105, 'Eve', 99000);
 
SELECT MAX(salary) AS second_highest_salary
FROM Employees
WHERE salary &lt; (
    SELECT MAX(salary)
    FROM Employees
 
);
▶ Run to see output

pyspark·

Sep 19, 2026Interview Question

Q.6

Calculate the average sales amount for each region.

Medium

Input Table: `Sales`

sales_id	region	sales_amount
501	North	50000
502	South	70000
503	North	80000
504	West	90000

I group the sales records by region using GROUP BY, and then use the AVG() aggregate function to calculate the average sales amount for each region.

CREATE TABLE Sales (
    sales_id INT,
    region VARCHAR(50),
    sales_amount DECIMAL(10, 2)
);
INSERT INTO Sales (sales_id, region, sales_amount)
VALUES
    (501, 'North', 50000),
    (502, 'South', 70000),
    (503, 'North', 80000),
 
    (504, 'West', 90000);
 
SELECT
    region,
    AVG(sales_amount) AS avg_sales
FROM Sales
 
GROUP BY region;
▶ Run to see output

pyspark·

Sep 19, 2026Interview Question

Q.7

Write a SQL query to fetch all orders that were placed on weekends (Saturday or Sunday).?

Medium

Input table: `Orders`

order_id	customer_id	order_date
401	1	2024-02-17
402	2	2024-02-18
403	3	2024-02-19
404	1	2024-02-24

Let's identify the days:

order_id	order_date	Day	Weekend?
401	2024-02-17	Saturday	✅
402	2024-02-18	Sunday	✅
403	2024-02-19	Monday	❌
404	2024-02-24	Saturday	✅

I use the DAYOFWEEK() function to determine the weekday for each order date, and then filter for Sunday and Saturday using IN (1, 7).

CREATE TABLE Orders (
    order_id INT,
    customer_id INT,
    order_date DATE
);
INSERT INTO Orders (order_id, customer_id, order_date)
VALUES
    (401, 1, '2024-02-17'),
    (402, 2, '2024-02-18'),
    (403, 3, '2024-02-19'),
 
    (404, 1, '2024-02-24');
 
SELECT
    order_id,
    customer_id,
    order_date
FROM Orders
WHERE DAYOFWEEK(order_date) IN (1, 7);
▶ Run to see output

pyspark·

Sep 19, 2026Interview Question

Q.8

Write a query to retrieve the first and last purchase date for each customer.?

Medium

Input Table: Transactions

transaction_id	customer_id	purchase_date
301	1	2024-01-10
302	2	2024-01-12
303	1	2024-02-15
304	2	2024-02-20
305	1	2024-03-05

CREATE TABLE Transactions (
    transaction_id INT,
    customer_id INT,
    purchase_date DATE
);
INSERT INTO Transactions
    (transaction_id, customer_id, purchase_date)
VALUES
    (301, 1, '2024-01-10'),
    (302, 2, '2024-01-12'),
    (303, 1, '2024-02-15'),
    (304, 2, '2024-02-20'),
 
    (305, 1, '2024-03-05');
 
SELECT
    customer_id,
    MIN(purchase_date) AS first_purchase,
    MAX(purchase_date) AS last_purchase
FROM Transactions
 
GROUP BY customer_id;
▶ Run to see output

pyspark·

Sep 19, 2026Interview Question

Q.9

Find customers who have placed more than 5 orders in the last 30 days.?

Medium

Input Table: `Orders`

order_id	customer_id	order_date
201	1	2024-02-15
202	2	2024-02-10
203	1	2024-02-18
204	3	2024-02-20
205	1	2024-02-25
206	2	2024-02-27
207	1	2024-03-02

CREATE TABLE Orders (
    order_id INT,
    customer_id INT,
    order_date DATE
);
INSERT INTO Orders (order_id, customer_id, order_date)
VALUES
    (201, 1, '2024-02-15'),
    (202, 2, '2024-02-10'),
    (203, 1, '2024-02-18'),
    (204, 3, '2024-02-20'),
    (205, 1, '2024-02-25'),
    (206, 2, '2024-02-27'),
 
    (207, 1, '2024-03-02');
 
SELECT customer_id,
       COUNT(order_id) AS order_count
FROM Orders
WHERE order_date &gt;= CURRENT_DATE - INTERVAL 30 DAY
GROUP BY customer_id
HAVING COUNT(order_id) &gt; 5;
▶ Run to see output

pyspark·

Sep 19, 2026Interview Question

Q.10

Write a query to fetch the top 3 employees with the highest salaries from an Employees table.?(Asked in Accenture)

Easy

Fetch the Top 3 Employees with the Highest Salaries

Input Table: Employees

emp_id	emp_name	salary
101	Alice	95000
102	Bob	87000
103	Charlie	91000
104	David	75000
105	Eve	99000

CREATE TABLE Employees (
    emp_id INT,
    emp_name VARCHAR(100),
    salary DECIMAL(10, 2)
);
INSERT INTO Employees (emp_id, emp_name, salary)
VALUES
    (101, 'Alice', 95000),
    (102, 'Bob', 87000),
    (103, 'Charlie', 91000),
    (104, 'David', 75000),
 
    (105, 'Eve', 99000);
SELECT emp_id, emp_name, salary
 
FROM Employees;
▶ Run to see output

SQL Interview Questions

SQL Interview Question: A Query Taking 2 Minutes Now Takes 20 Minutes. What Will You Do?

Fetch all orders where the total_value is greater than the average order value.?

Input Table: Orders

Find the most frequently sold product in each category.?

SQL concept

Find customers who have never placed an order.?

1. Customers Table

2. Orders Table

Find the second-highest salary from the Employees table without using LIMIT or TOP.

Example Employees Table

Calculate the average sales amount for each region.

Input Table: Sales

Write a SQL query to fetch all orders that were placed on weekends (Saturday or Sunday).?

Input table: Orders

Write a query to retrieve the first and last purchase date for each customer.?

Find customers who have placed more than 5 orders in the last 30 days.?

Input Table: Orders

Write a query to fetch the top 3 employees with the highest salaries from an Employees table.?(Asked in Accenture)

SQL
Interview Questions

Input Table: `Orders`

Input Table: `Sales`

Input table: `Orders`

Input Table: `Orders`