GREATEST and LEAST in MySQL

Introduction

GREATEST and LEAST help you find the biggest or smallest value from a list of values easily.

When you want to compare multiple numbers and pick the highest one.

When you want to find the smallest value among several columns in a table.

When you need to decide between different options based on their values.

When you want to simplify your query by avoiding multiple IF or CASE statements.

Syntax

MySQL

GREATEST(value1, value2, ..., valueN)
LEAST(value1, value2, ..., valueN)

You can use any number of values inside the parentheses.

Values can be columns, constants, or expressions.

Examples

Returns the largest number among 10, 20, and 30.

MySQL

SELECT GREATEST(10, 20, 30);

Returns the smallest number among 10, 20, and 30.

MySQL

SELECT LEAST(10, 20, 30);

Finds the highest value among price, discount, and 100 for each product.

MySQL

SELECT GREATEST(price, discount, 100) FROM products;

Finds the lowest score among three columns for each exam record.

MySQL

SELECT LEAST(score1, score2, score3) FROM exams;

Sample Program

This creates a table with students' scores in three subjects. Then it shows each student's highest and lowest score using GREATEST and LEAST.

MySQL

CREATE TABLE test_scores (
  student VARCHAR(20),
  math INT,
  science INT,
  english INT
);

INSERT INTO test_scores VALUES
('Alice', 85, 90, 78),
('Bob', 70, 65, 80),
('Charlie', 95, 88, 92);

SELECT student, 
       GREATEST(math, science, english) AS highest_score, 
       LEAST(math, science, english) AS lowest_score
FROM test_scores;

Important Notes

If any value is NULL, the result of GREATEST or LEAST will be NULL.

All values are compared as the same type, so mixing strings and numbers may give unexpected results.

Summary

GREATEST returns the largest value from a list.

LEAST returns the smallest value from a list.

They simplify comparing multiple values in SQL queries.

Practice

1. What does the MySQL function GREATEST(3, 7, 5) return?

easy

A. NULL

B. 3

C. 5

D. 7

Solution

1. Step 1: Understand the GREATEST function

   The GREATEST function returns the largest value among the given arguments.

2. Step 2: Compare the values 3, 7, and 5

   Among 3, 7, and 5, the largest number is 7.

3. Final Answer:

   7 -> Option D

4. Quick Check:

   GREATEST(3, 7, 5) = 7 [OK]

Hint: GREATEST picks the highest number from the list [OK]

Common Mistakes:

• Confusing GREATEST with LEAST
• Thinking it returns the first value
• Assuming it returns a sum

2. Which of the following is the correct syntax to find the smallest value among 10, 20, and 5 using MySQL?

easy

A. MIN(10, 20, 5)

B. LEAST(10, 20, 5)

C. SMALLEST(10, 20, 5)

D. LOWEST(10, 20, 5)

Solution

1. Step 1: Recall the function to find smallest value

   In MySQL, the LEAST function returns the smallest value from a list of arguments.

2. Step 2: Check the syntax options

   LEAST(10, 20, 5) is the correct syntax. MIN is an aggregate function and requires a column, not a list of values. SMALLEST and LOWEST are not valid MySQL functions.

3. Final Answer:

   LEAST(10, 20, 5) -> Option B

4. Quick Check:

   LEAST(10, 20, 5) is correct syntax [OK]

Hint: Use LEAST() for smallest, GREATEST() for largest values [OK]

Common Mistakes:

• Using MIN() with values instead of columns
• Using non-existent functions like SMALLEST()
• Confusing function names

3. Given the table Scores with columns math, science, and english, what will the query SELECT GREATEST(math, science, english) AS top_score FROM Scores WHERE id = 1; return if the row with id = 1 has values (85, 90, 88)?

medium

A. 90

B. 85

C. 88

D. NULL

Solution

1. Step 1: Identify the values for id = 1

   The row has math=85, science=90, english=88.

2. Step 2: Apply GREATEST to these values

   GREATEST(85, 90, 88) returns the largest value, which is 90.

3. Final Answer:

   90 -> Option A

4. Quick Check:

   GREATEST(85, 90, 88) = 90 [OK]

Hint: GREATEST returns the highest among given column values [OK]

Common Mistakes:

• Selecting the first column value instead of greatest
• Confusing GREATEST with LEAST
• Assuming NULL if any value is less

4. Consider this query: SELECT LEAST(score1, score2, score3) FROM Results; It returns NULL for some rows even though all scores are numbers. What is the likely cause?

medium

A. Syntax error in the query

B. LEAST function only works with positive numbers

C. One or more scores are NULL in those rows

D. LEAST returns the largest value, so NULL is unexpected

Solution

1. Step 1: Understand LEAST behavior with NULLs

   LEAST returns NULL if any argument is NULL because NULL means unknown value.

2. Step 2: Check the cause of NULL results

   If some rows have NULL in score1, score2, or score3, LEAST will return NULL for those rows.

3. Final Answer:

   One or more scores are NULL in those rows -> Option C

4. Quick Check:

   LEAST returns NULL if any input is NULL [OK]

Hint: Check for NULLs in inputs; LEAST returns NULL if any argument is NULL [OK]

Common Mistakes:

• Assuming LEAST ignores NULLs
• Thinking LEAST only works with positive numbers
• Misreading LEAST as GREATEST

5. You want to find the highest and lowest scores among three exams for each student in a table Students with columns exam1, exam2, and exam3. Which query correctly returns the student ID, highest score as max_score, and lowest score as min_score?

hard

A. SELECT student_id, GREATEST(exam1, exam2, exam3) AS max_score, LEAST(exam1, exam2, exam3) AS min_score FROM Students;

B. SELECT student_id, MAX(exam1, exam2, exam3) AS max_score, MIN(exam1, exam2, exam3) AS min_score FROM Students;

C. SELECT student_id, GREATEST(exam1, exam2, exam3) AS min_score, LEAST(exam1, exam2, exam3) AS max_score FROM Students;

D. SELECT student_id, MAX(exam1, exam2, exam3) AS min_score, MIN(exam1, exam2, exam3) AS max_score FROM Students;

Solution

1. Step 1: Understand GREATEST and LEAST usage

   GREATEST returns the highest value among columns, LEAST returns the lowest.

2. Step 2: Check the query syntax

   SELECT student_id, GREATEST(exam1, exam2, exam3) AS max_score, LEAST(exam1, exam2, exam3) AS min_score FROM Students; correctly uses GREATEST and LEAST with column names and aliases them properly. MAX and MIN are aggregate functions and cannot take multiple columns as arguments directly.

3. Final Answer:

   Option A query -> Option A

4. Quick Check:

   Use GREATEST and LEAST for column-wise max/min [OK]

Hint: Use GREATEST/LEAST for row-wise max/min, not MAX/MIN [OK]

Common Mistakes:

• Using MAX/MIN with multiple columns incorrectly
• Swapping GREATEST and LEAST aliases
• Syntax errors with aggregate functions