ROUND, CEIL, FLOOR in MySQL - Step-by-Step Execution

Concept Flow - ROUND, CEIL, FLOOR

Start with a number

↓

ROUND

↓

Round to nearest

↓

Return result

↓

End

Start with a number, pick ROUND to round normally, CEIL to round up, or FLOOR to round down, then get the result.

Execution Sample

MySQL

SELECT ROUND(4.3), CEIL(4.3), FLOOR(4.3);

This query rounds 4.3 normally, rounds it up, and rounds it down.

Execution Table

Step	Function	Input	Operation	Result
1	ROUND	4.3	Round to nearest integer	4
2	CEIL	4.3	Round up to next integer	5
3	FLOOR	4.3	Round down to previous integer	4
4	END		All functions executed	Query returns (4, 5, 4)

💡 All functions processed, query returns final rounded values.

Variable Tracker

Variable	Start	After ROUND	After CEIL	After FLOOR	Final
number	4.3	4.3	4.3	4.3	4.3
ROUND_result	N/A	4	4	4	4
CEIL_result	N/A	N/A	5	5	5
FLOOR_result	N/A	N/A	N/A	4	4

Key Moments - 3 Insights

Why does ROUND(4.3) return 4 instead of 5?

ROUND rounds to the nearest integer. Since 4.3 is closer to 4 than 5, it returns 4 (see execution_table row 1).

Why does CEIL(4.3) return 5 even though 4.3 is less than 5?

CEIL always rounds up to the next integer, so it returns 5 regardless of decimal part (see execution_table row 2).

Why does FLOOR(4.3) return 4 instead of 3?

FLOOR always rounds down to the previous integer, so it returns 4 because 4 is the greatest integer less than or equal to 4.3 (see execution_table row 3).

Visual Quiz - 3 Questions

Look at the execution_table, what is the result of CEIL(4.3) at step 2?

A 4

B 5

C 3

D 4.3

💡 Hint

Check the 'Result' column in execution_table row 2 for CEIL function.

At which step does the function round the number down?

A Step 3

B Step 2

C Step 1

D Step 4

💡 Hint

Look for FLOOR function in execution_table which rounds down.

If the input number was 4.7, what would ROUND(4.7) return?

A 4

B 6

C 5

D 4.7

💡 Hint

ROUND rounds to nearest integer; 4.7 is closer to 5 than 4.

Concept Snapshot

ROUND(number): rounds to nearest integer.
CEIL(number): rounds up to next integer.
FLOOR(number): rounds down to previous integer.
Use these to control decimal rounding in queries.
Example: SELECT ROUND(4.3), CEIL(4.3), FLOOR(4.3);

Full Transcript

This visual shows how MySQL rounding functions work step-by-step. Starting with the number 4.3, ROUND returns 4 because it rounds to the nearest integer. CEIL returns 5 because it always rounds up. FLOOR returns 4 because it always rounds down. The execution table tracks each function's input, operation, and result. The variable tracker shows how the number changes after each function. Key moments clarify common confusions about rounding behavior. The quiz tests understanding by asking about specific steps and results. Remember, ROUND is normal rounding, CEIL is always up, and FLOOR is always down.

Practice

1. Which MySQL function rounds a number to the nearest whole number or specified decimal place?

easy

A. CEIL

B. ROUND

C. FLOOR

D. TRUNCATE

Solution

1. Step 1: Understand the function purpose

   ROUND changes a number to the nearest integer or decimal place, unlike CEIL or FLOOR which only round up or down.

2. Step 2: Compare with other functions

   CEIL always rounds up, FLOOR always rounds down, TRUNCATE cuts decimals without rounding.

3. Final Answer:

   ROUND -> Option B

4. Quick Check:

   ROUND = nearest rounding [OK]

Hint: ROUND = nearest number, CEIL up, FLOOR down [OK]

Common Mistakes:

• Confusing CEIL with ROUND
• Thinking FLOOR rounds to nearest
• Assuming TRUNCATE rounds

2. Which of the following is the correct syntax to round the number 3.14159 to 2 decimal places in MySQL?

easy

A. ROUND(3.14159, 2)

B. CEIL(3.14159, 2)

C. FLOOR(3.14159, 2)

D. ROUND(3.14159. 2)

Solution

1. Step 1: Check function usage

   ROUND accepts two arguments: the number and the decimal places to round to.

2. Step 2: Identify correct syntax

   ROUND(3.14159, 2) is correct; CEIL and FLOOR do not take decimal places, and ROUND(3.14159. 2) has a syntax error with a dot instead of a comma.

3. Final Answer:

   ROUND(3.14159, 2) -> Option A

4. Quick Check:

   ROUND(number, decimals) syntax [OK]

Hint: ROUND(number, decimals) uses comma, CEIL/FLOOR no decimals [OK]

Common Mistakes:

• Using CEIL or FLOOR with decimal places
• Using dot instead of comma between arguments
• Missing second argument for ROUND

3. What is the result of the query: SELECT CEIL(4.2), FLOOR(4.8), ROUND(4.5);?

medium

A. 5, 4, 5

B. 4, 4, 4

C. 5, 5, 5

D. 4, 5, 4

Solution

1. Step 1: Evaluate CEIL(4.2)

   CEIL rounds up to the next whole number, so CEIL(4.2) = 5.

2. Step 2: Evaluate FLOOR(4.8) and ROUND(4.5)

   FLOOR rounds down, so FLOOR(4.8) = 4. ROUND rounds to nearest integer, 4.5 rounds up to 5.

3. Final Answer:

   5, 4, 5 -> Option A

4. Quick Check:

   CEIL=5, FLOOR=4, ROUND=5 [OK]

Hint: CEIL up, FLOOR down, ROUND nearest (0.5 rounds up) [OK]

Common Mistakes:

• Thinking FLOOR(4.8) is 5
• Rounding 4.5 down instead of up
• Confusing CEIL and FLOOR

4. Identify the error in this query: SELECT CEIL(5.7, 1), FLOOR(3.2), ROUND(2.718);

medium

A. ROUND requires two arguments

B. FLOOR requires two arguments

C. CEIL does not accept two arguments

D. No error, query is correct

Solution

1. Step 1: Check CEIL function arguments

   CEIL only accepts one argument (the number). Passing two arguments causes an error.

2. Step 2: Verify FLOOR and ROUND usage

   FLOOR accepts one argument, ROUND can accept one or two arguments. Both FLOOR(3.2) and ROUND(2.718) are valid.

3. Final Answer:

   CEIL does not accept two arguments -> Option C

4. Quick Check:

   CEIL = 1 argument only [OK]

Hint: CEIL/FLOOR take 1 argument; ROUND can take 1 or 2 [OK]

Common Mistakes:

• Passing two arguments to CEIL or FLOOR
• Assuming ROUND always needs two arguments
• Thinking query has no errors

5. You have a table prices with a column cost containing decimal values. You want to create a new column rounded_cost that rounds cost to the nearest integer but always rounds up if the decimal part is exactly 0.5. Which MySQL expression achieves this?

hard

A. ROUND(cost)

B. IF(cost - FLOOR(cost) = 0.5, FLOOR(cost), ROUND(cost))

C. CEIL(cost - 0.5)

D. CEIL(cost)

Solution

1. Step 1: Understand rounding rules

   In MySQL, ROUND rounds to nearest integer; halfway cases (.5) round away from zero (up for positive numbers).

2. Step 2: Select the correct expression

   CEIL(cost) always rounds up, so it rounds up when decimal part is exactly 0.5, fulfilling the requirement.

3. Step 3: Analyze other options

   A rounds .5 up normally, but does not always round up if decimal is exactly 0.5 (it rounds to nearest). B rounds down for exactly .5, which is incorrect. D fails on .5 cases as CEIL(cost - 0.5) can round down.

4. Final Answer:

   CEIL(cost) -> Option D

5. Quick Check:

   CEIL(cost) always rounds up [OK]

Hint: CEIL(cost) always rounds up, including .5 cases [OK]

Common Mistakes:

• Assuming ROUND always rounds .5 up as needed
• Using conditional that rounds .5 down
• CEIL(cost - 0.5) fails on .5 cases