MIN and MAX functions in SQL - Mini Project: Build & Apply

Finding Minimum and Maximum Values with SQL

📖 Scenario: You are working with a small store's sales database. The store wants to find out the lowest and highest prices of products they sell to help with pricing decisions.

🎯 Goal: Build SQL queries that use the MIN and MAX functions to find the lowest and highest product prices from the products table.

📋 What You'll Learn

Create a products table with columns product_id, product_name, and price.

Insert exactly three products with specified prices.

Write a query to find the minimum price using the MIN function.

Write a query to find the maximum price using the MAX function.

💡 Why This Matters

🌍 Real World

Stores and businesses often need to find the lowest and highest prices of products to set discounts or price ranges.

💼 Career

Knowing how to use MIN and MAX functions is essential for data analysis and reporting roles that work with databases.

1

Create the products table and insert data

Write SQL statements to create a table called products with columns product_id (integer), product_name (text), and price (integer). Then insert these three rows exactly: (1, 'Pen', 10), (2, 'Notebook', 25), (3, 'Eraser', 5).

SQL

-- Create the products table and insert the three products
-- Your code here

Hint

Use CREATE TABLE to define the table and INSERT INTO to add rows.

2

Set up a query to find the minimum price

Write a SQL query that selects the minimum price from the products table using the MIN function. Name the result column lowest_price.

SQL

CREATE TABLE products (
    product_id INTEGER,
    product_name TEXT,
    price INTEGER
);

INSERT INTO products (product_id, product_name, price) VALUES
(1, 'Pen', 10),
(2, 'Notebook', 25),
(3, 'Eraser', 5);

-- Write a query to find the minimum price
-- Your code here

Hint

Use SELECT MIN(price) AS lowest_price FROM products; to get the lowest price.

3

Write a query to find the maximum price

Write a SQL query that selects the maximum price from the products table using the MAX function. Name the result column highest_price.

SQL

CREATE TABLE products (
    product_id INTEGER,
    product_name TEXT,
    price INTEGER
);

INSERT INTO products (product_id, product_name, price) VALUES
(1, 'Pen', 10),
(2, 'Notebook', 25),
(3, 'Eraser', 5);

SELECT MIN(price) AS lowest_price FROM products;

-- Write a query to find the maximum price
-- Your code here

Hint

Use SELECT MAX(price) AS highest_price FROM products; to get the highest price.

4

Combine minimum and maximum price queries

Write a single SQL query that selects both the minimum and maximum prices from the products table. Name the columns lowest_price and highest_price respectively.

SQL

CREATE TABLE products (
    product_id INTEGER,
    product_name TEXT,
    price INTEGER
);

INSERT INTO products (product_id, product_name, price) VALUES
(1, 'Pen', 10),
(2, 'Notebook', 25),
(3, 'Eraser', 5);

SELECT MIN(price) AS lowest_price FROM products;

SELECT MAX(price) AS highest_price FROM products;

-- Write a query to select both minimum and maximum prices together
-- Your code here

Hint

Use both MIN(price) and MAX(price) in the same SELECT statement.

Practice

1. What does the SQL function MIN() do when applied to a column of numbers?

easy

A. Calculates the average of the numbers

B. Finds the largest number in the column

C. Finds the smallest number in the column

D. Counts the total numbers in the column

Solution

1. Step 1: Understand the purpose of MIN()

   The MIN() function is designed to find the smallest value in a column of data.

2. Step 2: Compare with other functions

   Unlike MAX() which finds the largest, or AVG() which calculates average, MIN() specifically returns the minimum value.

3. Final Answer:

   Finds the smallest number in the column -> Option C

4. Quick Check:

   MIN() = smallest value [OK]

Hint: MIN() always returns the smallest value in a column [OK]

Common Mistakes:

• Confusing MIN() with MAX()
• Thinking MIN() calculates average
• Using MIN() to count rows

2. Which of the following is the correct syntax to find the maximum salary from a table named Employees?

easy

A. SELECT MAX salary FROM Employees;

B. SELECT MAX{salary} FROM Employees;

C. SELECT MAX[salary] FROM Employees;

D. SELECT MAX(salary) FROM Employees;

Solution

1. Step 1: Recall correct function syntax

   The correct syntax for SQL aggregate functions like MAX() requires parentheses around the column name.

2. Step 2: Check syntax

   SELECT MAX(salary) FROM Employees; uses MAX(salary) which is correct. Forms without parentheses or using [] {} are invalid.

3. Final Answer:

   SELECT MAX(salary) FROM Employees; -> Option D

4. Quick Check:

   MAX() uses parentheses around column [OK]

Hint: Use parentheses around column name in MAX() [OK]

Common Mistakes:

• Omitting parentheses in function calls
• Using square or curly brackets instead of parentheses
• Misspelling function names

3. Given the table Products with a column Price containing values (100, 250, 50, 400), what will the query SELECT MIN(Price), MAX(Price) FROM Products; return?

medium

A. (400, 50)

B. (50, 400)

C. (100, 250)

D. (0, 400)

Solution

1. Step 1: Identify minimum price

   From the values (100, 250, 50, 400), the smallest price is 50.

2. Step 2: Identify maximum price

   The largest price in the list is 400.

3. Final Answer:

   (50, 400) -> Option B

4. Quick Check:

   MIN = 50, MAX = 400 [OK]

Hint: MIN returns smallest, MAX returns largest value [OK]

Common Mistakes:

• Mixing up MIN and MAX values
• Assuming default zero minimum
• Confusing order of returned values

4. What is wrong with this query to find the maximum age from the Users table?
SELECT MAX age FROM Users;

medium

A. Missing parentheses around the column name

B. MAX function cannot be used on numeric columns

C. Table name should be in quotes

D. MAX should be lowercase

Solution

1. Step 1: Check function syntax

   The MAX() function requires parentheses around the column name, so MAX age is invalid syntax.

2. Step 2: Verify other options

   MAX works on numeric columns, table names don't need quotes, and function names are case-insensitive in SQL.

3. Final Answer:

   Missing parentheses around the column name -> Option A

4. Quick Check:

   MAX() needs parentheses [OK]

Hint: Always use parentheses with MAX() [OK]

Common Mistakes:

• Omitting parentheses in function calls
• Thinking MAX() only works on strings
• Adding unnecessary quotes around table names

5. You have a table Orders with columns OrderID, CustomerID, and TotalAmount. How would you write a query to find the highest order amount for each customer?

hard

A. SELECT CustomerID, MAX(TotalAmount) FROM Orders GROUP BY CustomerID;

B. SELECT MAX(TotalAmount) FROM Orders WHERE CustomerID;

C. SELECT CustomerID, MAX(TotalAmount) FROM Orders;

D. SELECT CustomerID, TotalAmount FROM Orders WHERE MAX(TotalAmount);

Solution

1. Step 1: Understand grouping requirement

   To find the highest order amount per customer, we must group data by CustomerID.

2. Step 2: Use MAX() with GROUP BY

   Using MAX(TotalAmount) with GROUP BY CustomerID returns the maximum order amount for each customer.

3. Step 3: Why others fail

   Using MAX() in a WHERE clause is invalid, WHERE CustomerID; is meaningless, and selecting CustomerID with MAX() without GROUP BY causes an error because CustomerID is not aggregated.

4. Final Answer:

   SELECT CustomerID, MAX(TotalAmount) FROM Orders GROUP BY CustomerID; -> Option A

5. Quick Check:

   Use GROUP BY with MAX() for per-group max [OK]

Hint: Use GROUP BY with MAX() to get max per group [OK]

Common Mistakes:

• Forgetting GROUP BY when using MAX per group
• Using MAX() in WHERE clause incorrectly
• Selecting columns without grouping