Sunday, September 17, 2023

How to use rank, row_number, and dense_rank in SQL? Example

 Hey folks, ever found yourself at a data party, trying to figure out the pecking order? Well, I've been there too, and SQL has some nifty moves to help you out. Today, I'm going to show you how to use RANK, ROW_NUMBER, and DENSE_RANK in SQL to sort and analyze your data like a pro.

How to use rank, row_number, and dense_rank in SQL? Example

Now, let's see the step by step guide to learn how to use ranking function in Java like rank, row_number, and dense_rank

Getting the Basics Right

Let's start with the fundamentals. These three functions—RANK, ROW_NUMBER, and DENSE_RANK—help you assign a rank to each row in your result set. They're like the party host who tells you where you stand in the VIP list.

ROW_NUMBER: Every Row Gets a Number

ROW_NUMBER() is your go-to when you need a unique number assigned to each row. It's like handing out party tickets with sequential numbers. Here's how you use it:

SELECT name, age, ROW_NUMBER() OVER (ORDER BY age) AS row_num
FROM guests;

This query ranks your guests by age, and each guest gets their own row number.

RANK: Sharing Ranks with Grace

Now, imagine you have guests with the same age, and you want to assign the same rank to them, followed by the next rank. RANK() does that elegantly. Check this out:

SELECT name, age, RANK() OVER (ORDER BY age) AS rank
FROM guests;

RANK() gives guests with the same age the same rank and then skips to the next rank.

DENSE_RANK: No Skipping Allowed

DENSE_RANK(), on the other hand, is like RANK() but without the skipping part. It's as if it's saying, "Let's keep it dense; no gaps in the ranks!" Here's how you use it:

SELECT name, age, DENSE_RANK() OVER (ORDER BY age) AS dense_rank
FROM guests;

DENSE_RANK() assigns the same rank to guests with the same age, just like RANK(), but without any gaps.

Partitioning Your Data

Imagine you're at a party with multiple rooms, and you want to rank guests separately within each room. That's where PARTITION BY comes in. It's like telling SQL to create separate VIP lists for each room.

SELECT room, name, age, RANK() OVER (PARTITION BY room ORDER BY age) AS rank
FROM guests;

With PARTITION BY, you rank guests by age, but separately for each room.

Ties and Handling Them

Life (and data) can be messy, and you might encounter situations where multiple rows have the same value. ROW_NUMBER, RANK, and DENSE_RANK handle ties differently.

ROW_NUMBER assigns a unique number to each row, even if they have the same value.
RANK gives the same rank to rows with the same value but skips the next rank.
DENSE_RANK assigns the same rank to rows with the same value and doesn't skip ranks.

Practical Applications

Now that you know the dance steps, let's talk about how you can use these functions in real-life scenarios.

Top Performers: Use RANK() to find the top-performing salespeople, students, or athletes based on their scores or achievements.

SELECT name, score, RANK() OVER (ORDER BY score DESC) AS rank
FROM performers;

Pagination: ROW_NUMBER() is fantastic for pagination. Displaying a limited number of results on each page of a website? ROW_NUMBER() helps you achieve that.

SELECT product_name, price
FROM products

Customer Loyalty Tiers: Assigning loyalty tiers to customers based on their purchase history? DENSE_RANK() comes to the rescue.

SELECT customer_name, total_purchase_amount,
       DENSE_RANK() OVER (ORDER BY total_purchase_amount DESC) AS loyalty_tier
FROM customers;

Performance Considerations

While these functions are fantastic for ranking, be mindful of their performance when dealing with large datasets. Overusing them can slow down your queries, so use them wisely.

Handling Ties with Style

Ties can be common in real-world data, and it's crucial to know how these functions handle tie-breaking. Let's say you have a competition with tied scores:

SELECT participant, score, RANK() OVER (ORDER BY score DESC) AS rank 
FROM competition;

With RANK(), if two participants have the same score, they both get the same rank, and the next rank is skipped. For example, if two participants tie for first place, the next participant will be ranked third.

SELECT participant, score, DENSE_RANK() OVER (ORDER BY score DESC) AS dense_rank
FROM competition;

On the other hand, DENSE_RANK() handles ties gracefully. It assigns the same rank to participants with tied scores, but it doesn't skip ranks. So, in the case of a tie for first place, the next participant will still be ranked second.

Dealing with Null Values

What if your data has some missing values (NULLs)? These ranking functions are flexible enough to handle them. By default, NULL values get the lowest possible rank. So, if you have participants with NULL scores in your competition, they'll be ranked at the bottom.

SELECT participant, score, RANK() OVER (ORDER BY score DESC) AS rank
FROM competition;

If you want NULL values to be ranked last, you can use the following query:

SELECT participant, score, RANK() OVER (ORDER BY score DESC NULLS LAST) AS rank
FROM competition;

This query ensures that NULL scores are assigned the highest rank possible.

Ranking Within Groups

Sometimes, you'll need to rank data within groups. Imagine you have data on students' scores in different subjects, and you want to rank them within each subject. You can use PARTITION BY for this:

SELECT subject, student, score,
       RANK() OVER (PARTITION BY subject ORDER BY score DESC) AS rank
FROM student_scores;

This query creates separate ranking lists for each subject, ensuring that students are ranked within their respective subject groups.

Practical Use Cases

Now that you've got a strong grasp of RANK, ROW_NUMBER, and DENSE_RANK, let's explore some real-world use cases.

Sports Leaderboards: Whether you're tracking the best players in a video game or the top athletes in a sports league, these ranking functions help you create dynamic leaderboards.

Financial Analysis: In finance, you can use these functions to rank investments, clients, or transactions based on various metrics such as returns, portfolio sizes, or transaction values.

Employee Performance: HR departments often use ranking functions to assess employee performance and assign performance ratings or bonuses accordingly.

E-commerce Recommendations: RANK, ROW_NUMBER, and DENSE_RANK can be used to rank products for recommendation engines, helping e-commerce platforms suggest products based on customer preferences and historical data.

Performance Optimization

While these functions are incredibly versatile, remember that they can impact query performance, especially with large datasets. If you're dealing with massive amounts of data, consider using appropriate indexing and optimizations to keep your queries snappy.

Wrapping Up

And there you have it! With RANK, ROW_NUMBER, and DENSE_RANK in your SQL repertoire, you can navigate your data parties like a pro. Whether you're ranking guests at a party or finding the top performers in your business, these functions have got you covered. So, go ahead and let your data dance begin!

Other SQL articles you may like:

Quiz Time

  • What is the primary purpose of the SQL functions RANK(), ROW_NUMBER(), and DENSE_RANK()?

A) To calculate the average of a set of values.
B) To perform arithmetic calculations.
C) To assign a unique identifier to each row in a result set.
D) To retrieve data from multiple tables.

  • Which of the following SQL functions assigns a unique incremental integer value to each row in the result set?


  • In SQL, when would you typically use RANK() instead of ROW_NUMBER() or DENSE_RANK()?

A) When you need to rank rows based on their position in the result set.
B) When you need to assign the same rank to rows with equal values.
C) When you need to calculate the total number of rows in a table.
D) When you need to count the number of distinct values in a column.

No comments:

Post a Comment