RANK and DENSE_RANK difference in SQL - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does the RANK() function do in SQL?

RANK() assigns a rank number to each row within a partition of a result set, with gaps in ranking when there are ties.

beginner

How does DENSE_RANK() differ from RANK() in SQL?

DENSE_RANK() assigns ranks without gaps, so tied rows get the same rank and the next rank is the immediate next number.

intermediate

If two rows tie for rank 2, what rank will the next row get with RANK()?

The next row will get rank 4, because RANK() leaves gaps after ties.

intermediate

If two rows tie for rank 2, what rank will the next row get with DENSE_RANK()?

The next row will get rank 3, because DENSE_RANK() does not leave gaps after ties.

intermediate

Why might you choose DENSE_RANK() over RANK()?

Choose DENSE_RANK() when you want continuous ranking numbers without gaps, useful for compact ranking lists.

What happens to the rank numbers after a tie when using RANK()?

A They skip numbers creating gaps

B They assign the same rank to all rows

C They reset to 1

D They continue without gaps

RANK() skips rank numbers after ties, creating gaps.

Which function assigns ranks without gaps after ties?

A COUNT()

B ROW_NUMBER()

C RANK()

D DENSE_RANK()

DENSE_RANK() assigns ranks without gaps after ties.

If two rows tie for first place, what rank does the next row get with DENSE_RANK()?

A 3

B 2

C 1

D 4

DENSE_RANK() assigns the next rank as 2 after two tied rows at rank 1.

Which ranking function can produce gaps in the ranking sequence?

A RANK()

B DENSE_RANK()

C ROW_NUMBER()

D SUM()

RANK() produces gaps in ranking numbers after ties.

What is a key difference between RANK() and DENSE_RANK()?

A RANK() assigns unique ranks, DENSE_RANK() does not

B DENSE_RANK() leaves gaps, RANK() does not

C RANK() leaves gaps after ties, DENSE_RANK() does not

D Both assign ranks randomly

RANK() leaves gaps after ties; DENSE_RANK() assigns consecutive ranks without gaps.

Explain how RANK() and DENSE_RANK() handle ties differently in SQL.

Think about what happens to the next rank number after a tie.

Describe a scenario where you would prefer to use DENSE_RANK() instead of RANK().

Consider when gaps in ranking numbers might confuse users.

Practice

1. What is the main difference between RANK() and DENSE_RANK() functions in SQL?

easy

A. DENSE_RANK() assigns random ranks, RANK() assigns sequential ranks.

B. RANK() skips rank numbers after ties, DENSE_RANK() does not skip numbers.

C. RANK() and DENSE_RANK() always return the same results.

D. DENSE_RANK() skips rank numbers after ties, RANK() does not skip numbers.

Solution

1. Step 1: Understand how RANK() works with ties

   RANK() assigns the same rank to tied rows but skips the next rank numbers accordingly. For example, if two rows tie for rank 1, the next rank will be 3.

2. Step 2: Understand how DENSE_RANK() works with ties

   DENSE_RANK() also assigns the same rank to tied rows but does not skip rank numbers. So after two rows tied at rank 1, the next rank will be 2.

3. Final Answer:

   RANK() skips rank numbers after ties, DENSE_RANK() does not skip numbers. -> Option B

4. Quick Check:

   Skipping ranks = RANK() [OK]

Hint: Remember: RANK skips numbers after ties, DENSE_RANK does not [OK]

Common Mistakes:

• Thinking both functions behave the same with ties
• Confusing which function skips rank numbers
• Assuming ranks are assigned randomly

2. Which of the following is the correct syntax to get the rank of employees ordered by salary using DENSE_RANK()?

easy

A. SELECT employee_id, RANK() BY salary FROM employees;

B. SELECT employee_id, DENSE_RANK(salary) FROM employees ORDER BY salary DESC;

C. SELECT employee_id, DENSE_RANK() OVER (ORDER BY salary DESC) AS rank FROM employees;

D. SELECT employee_id, DENSE_RANK() ORDER BY salary FROM employees;

Solution

1. Step 1: Identify correct DENSE_RANK() syntax

   The correct syntax uses DENSE_RANK() OVER (ORDER BY column) to rank rows based on a column.

2. Step 2: Check each option

   SELECT employee_id, DENSE_RANK() OVER (ORDER BY salary DESC) AS rank FROM employees; uses the correct window function syntax. Options A, B, and D have syntax errors or misuse the function.

3. Final Answer:

   SELECT employee_id, DENSE_RANK() OVER (ORDER BY salary DESC) AS rank FROM employees; -> Option C

4. Quick Check:

   Window function syntax = SELECT employee_id, DENSE_RANK() OVER (ORDER BY salary DESC) AS rank FROM employees; [OK]

Hint: Use OVER (ORDER BY ...) with ranking functions [OK]

Common Mistakes:

• Omitting OVER clause
• Passing column inside function parentheses
• Using wrong keywords like BY instead of ORDER BY

3. Given the table Scores with values:
Player | Score
Alice | 100
Bob | 90
Carol | 90
Dave | 80
What will be the output of this query?

SELECT Player, Score, RANK() OVER (ORDER BY Score DESC) AS Rank, DENSE_RANK() OVER (ORDER BY Score DESC) AS DenseRank FROM Scores;

medium

A. [{"Player":"Alice","Score":100,"Rank":1,"DenseRank":1},{"Player":"Bob","Score":90,"Rank":2,"DenseRank":2},{"Player":"Carol","Score":90,"Rank":2,"DenseRank":2},{"Player":"Dave","Score":80,"Rank":4,"DenseRank":3}]

B. [{"Player":"Alice","Score":100,"Rank":1,"DenseRank":1},{"Player":"Bob","Score":90,"Rank":3,"DenseRank":2},{"Player":"Carol","Score":90,"Rank":3,"DenseRank":2},{"Player":"Dave","Score":80,"Rank":4,"DenseRank":3}]

C. [{"Player":"Alice","Score":100,"Rank":1,"DenseRank":1},{"Player":"Bob","Score":90,"Rank":2,"DenseRank":3},{"Player":"Carol","Score":90,"Rank":2,"DenseRank":3},{"Player":"Dave","Score":80,"Rank":3,"DenseRank":4}]

D. [{"Player":"Alice","Score":100,"Rank":1,"DenseRank":1},{"Player":"Bob","Score":90,"Rank":2,"DenseRank":2},{"Player":"Carol","Score":90,"Rank":3,"DenseRank":2},{"Player":"Dave","Score":80,"Rank":4,"DenseRank":3}]

Solution

1. Step 1: Assign RANK() values

   Alice has highest score 100, rank 1. Bob and Carol tie at 90, both get rank 2. Because of tie at rank 2, next rank is 4 for Dave.

2. Step 2: Assign DENSE_RANK() values

   Alice is dense rank 1. Bob and Carol tie at 90, dense rank 2. Dave has next dense rank 3 (no skipping).

3. Final Answer:

   [{"Player":"Alice","Score":100,"Rank":1,"DenseRank":1},{"Player":"Bob","Score":90,"Rank":2,"DenseRank":2},{"Player":"Carol","Score":90,"Rank":2,"DenseRank":2},{"Player":"Dave","Score":80,"Rank":4,"DenseRank":3}] -> Option A

4. Quick Check:

   RANK skips numbers, DENSE_RANK does not [OK]

Hint: Check how ranks jump after ties for RANK vs DENSE_RANK [OK]

Common Mistakes:

• Assigning dense ranks with gaps
• Not skipping ranks in RANK after ties
• Mixing up rank numbers for tied rows

4. You wrote this query:

SELECT name, RANK() ORDER BY score DESC FROM players;

But it gives a syntax error. What is the problem?

medium

A. Missing OVER() clause after RANK() function.

B. ORDER BY cannot be used inside SELECT clause.

C. RANK() requires a parameter inside parentheses.

D. The table name is missing in the query.

Solution

1. Step 1: Check RANK() function usage

   RANK() is a window function and must be followed by OVER() clause specifying order.

2. Step 2: Identify missing OVER() clause

   The query uses RANK() without OVER(), causing syntax error.

3. Final Answer:

   Missing OVER() clause after RANK() function. -> Option A

4. Quick Check:

   Window functions need OVER() [OK]

Hint: Always add OVER() after window functions like RANK() [OK]

Common Mistakes:

• Forgetting OVER() clause
• Trying to put ORDER BY inside SELECT without OVER()
• Assuming RANK() takes parameters

5. You have a sales table:
Salesperson | SalesAmount
John | 500
Jane | 700
Joe | 700
Jill | 600
You want to assign ranks so that tied salespeople share the same rank and the next rank number is not skipped. Which query correctly achieves this?

hard

A. SELECT Salesperson, SalesAmount, RANK() OVER (ORDER BY SalesAmount DESC) AS Rank FROM sales;

B. SELECT Salesperson, SalesAmount, RANK() OVER (PARTITION BY SalesAmount ORDER BY SalesAmount DESC) AS Rank FROM sales;

C. SELECT Salesperson, SalesAmount, ROW_NUMBER() OVER (ORDER BY SalesAmount DESC) AS Rank FROM sales;

D. SELECT Salesperson, SalesAmount, DENSE_RANK() OVER (ORDER BY SalesAmount DESC) AS Rank FROM sales;

Solution

1. Step 1: Understand ranking requirements

   Tied salespeople should share the same rank, and the next rank number should not skip any numbers.

2. Step 2: Choose correct function

   DENSE_RANK() assigns same rank to ties and does not skip ranks. RANK() skips ranks after ties. ROW_NUMBER() never assigns same rank to ties. SELECT Salesperson, SalesAmount, RANK() OVER (PARTITION BY SalesAmount ORDER BY SalesAmount DESC) AS Rank FROM sales; misuses PARTITION BY.

3. Final Answer:

   SELECT Salesperson, SalesAmount, DENSE_RANK() OVER (ORDER BY SalesAmount DESC) AS Rank FROM sales; -> Option D

4. Quick Check:

   DENSE_RANK() for no skipped ranks after ties [OK]

Hint: Use DENSE_RANK() to avoid skipping ranks after ties [OK]

Common Mistakes:

• Using RANK() when no skipping is wanted
• Using ROW_NUMBER() which never ties
• Incorrect use of PARTITION BY in ranking