MIN and MAX functions in SQL - Step-by-Step Execution

Concept Flow - MIN and MAX functions

Start with a column of values

↓

Apply MIN function

→Find smallest value

↓

Apply MAX function

→Find largest value

↓

Return result as single value

MIN finds the smallest value in a column, MAX finds the largest, both return one value.

Execution Sample

SQL

SELECT MIN(age) AS Youngest, MAX(age) AS Oldest FROM people;

This query finds the youngest and oldest ages from the people table.

Execution Table

Step	Action	Column Values	MIN Result	MAX Result
1	Read all ages	[23, 45, 31, 19, 40]
2	Find minimum age	[23, 45, 31, 19, 40]	19
3	Find maximum age	[23, 45, 31, 19, 40]	19	45
4	Return results		19	45

💡 All values processed, MIN and MAX results returned

Variable Tracker

Variable	Start	After Step 2	After Step 3	Final
ages	[23, 45, 31, 19, 40]	[23, 45, 31, 19, 40]	[23, 45, 31, 19, 40]	[23, 45, 31, 19, 40]
min_age	NULL	19	19	19
max_age	NULL	NULL	45	45

Key Moments - 2 Insights

Why does MIN return only one value even though there are many ages?

MIN scans all values but returns only the smallest one as a single result, as shown in execution_table step 2.

Can MIN and MAX be used on text columns?

Yes, MIN returns the alphabetically first value and MAX the last, similar to numeric values but based on sorting order.

Visual Quiz - 3 Questions

Look at the execution table, what is the MIN result after step 2?

A 23

B 45

C 19

D NULL

💡 Hint

Check the 'MIN Result' column at step 2 in the execution_table.

At which step does the MAX function find the largest value?

A Step 2

B Step 3

C Step 1

D Step 4

💡 Hint

Look at the 'MAX Result' column in the execution_table to see when MAX is assigned.

If the ages were all the same, what would MIN and MAX return?

A The same value

B NULL

C Different values

D Error

💡 Hint

MIN and MAX return the smallest and largest values respectively; if all values are equal, both return that value.

Concept Snapshot

MIN(column) returns the smallest value in a column.
MAX(column) returns the largest value.
Both return a single value.
Used to find extremes in data.
Works on numbers and text (alphabetical order).

Full Transcript

The MIN and MAX functions in SQL help find the smallest and largest values in a column. For example, given ages 23, 45, 31, 19, and 40, MIN returns 19 and MAX returns 45. The process reads all values, finds the minimum and maximum, then returns these as single results. These functions work on numbers and text, returning the smallest or largest based on sorting. They always return one value, even if many rows exist.

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