Adventures in Machine Learning

Mastering SQL Server’s DENSE_RANK() Function: Advanced Examples

In the world of database management, SQL Server is a widely used platform that offers various functions to ease data handling. One such function, DENSE_RANK(), is designed to rank values within a specified range.

In this article, we will explore DENSE_RANK() in detail, including an overview of the function, its syntax and parameters, and examples of how to use it effectively.

Overview of DENSE_RANK() Function

DENSE_RANK() is a SQL Server function that assigns rankings to a set of values within a specified range. The rankings are based on the values’ order and partitioning, making it easy to identify where these values stand in relation to one another.

Lets take an example of product ranking. Suppose if you want to rank products based on their price, DENSE_RANK() can be used to assign a rank to each product for their respective prices.

The rank assigned by DENSE_RANK() will depend on the product’s price, and higher-priced products will be given a higher rank.

Syntax and Parameters of DENSE_RANK() function

The syntax for using DENSE_RANK() function is quite simple. Below is an example of the syntax:

SELECT DENSE_RANK() OVER (PARTITION BY column_name ORDER BY column_name) AS ‘Ranking’

FROM table_name

The function comprises two main parameters: PARTITION BY and ORDER BY. PARTITION BY identifies a range of values within which DENSE_RANK() will rank the values based on their order.

ORDER BY specifies a column or columns based on which the ranking will be decided. In our previous example, we used Product prices as the basis for ranking.

Creating and Inserting Data into a Table

To illustrate DENSE_RANK() function effectively, let’s first create and insert data into the table. For this example, we will create a new table called ProductPrice with four columns: ProductID, ProductName, ListPrice, and Color.

To create a new table, execute the following code:

CREATE TABLE ProductPrice (

ProductID INT PRIMARY KEY,

ProductName VARCHAR(50),

ListPrice DECIMAL(8,2),

Color VARCHAR(20)

);

Once the table is created, insert data into the table using the INSERT INTO command:

INSERT INTO ProductPrice VALUES

(1, ‘Blue T-shirt’, 25.00, ‘Blue’),

(2, ‘Red Shirt’, 20.00, ‘Red’),

(3, ‘Black Pants’, 50.00, ‘Black’),

(4, ‘Green Cap’, 10.00, ‘Green’),

(5, ‘White Skirt’, 35.99, ‘White’),

(6, ‘Red Jeans’, 60.00, ‘Red’),

(7, ‘Pink Dress’, 45.50, ‘Pink’);

Examples of Using DENSE_RANK() Function

Now that our table is populated with data, let’s move on to some examples of how to use DENSE_RANK(). Example 1: Rank products by their price

To rank the products based on their prices, we can use the following code:

SELECT ProductName, ListPrice, DENSE_RANK() OVER (ORDER BY ListPrice DESC) AS ‘ProductRank’

FROM ProductPrice;

Here we have used DENSE_RANK() function to rank the products based on their prices, and we have ordered them in descending order. The output will look like:

ProductName ListPrice ProductRank

Red Jeans 60.00 1

Black Pants 50.00 2

White Skirt 35.99 3

Pink Dress 45.50 4

Blue T-shirt 25.00 5

Red Shirt 20.00 6

Green Cap 10.00 7

Example 2: Rank products by their color and price

To include a second parameter for ranking, in this case, product color, we can use the following code:

SELECT ProductName, ListPrice, Color, DENSE_RANK() OVER (PARTITION BY Color ORDER BY ListPrice DESC) AS ‘ProductRank’

FROM ProductPrice;

Here we have used PARTITION BY clause to identify the range of values, product color, within which DENSE_RANK() will rank the values based on their order, product prices. The output will look like:

ProductName ListPrice Color ProductRank

Green Cap 10.00 Green 1

White Skirt 35.99 White 1

Red Shirt 20.00 Red 1

Red Jeans 60.00 Red 2

Blue T-shirt 25.00 Blue 1

Pink Dress 45.50 Pink 1

Black Pants 50.00 Black 1

Conclusion:

In conclusion, DENSE_RANK() is a powerful function that facilitates ranking values within a specified range. It is widely used in SQL Server to rank and categorize data.

By understanding the syntax and parameters of DENSE_RANK(), one can quickly apply this function to rank values in their database.In the previous sections, we have discussed the DENSE_RANK() function in SQL Server, including its syntax and parameters, and provided examples of how to use it for ranking values within a specified range. In this article, we will continue exploring the DENSE_RANK() function, but this time, with a focus on more advanced examples.

Specifically, we will look at two scenarios where DENSE_RANK() can be applied to complex result sets and partitions.

Using DENSE_RANK() over a Result Set

Suppose you want to rank products based on their price, and you have two tables that contain the necessary data for the product names and list prices. One table contains a list of products and another a list of their corresponding prices.

You want to join these tables on the product ID to get a list of products with their respective prices and rankings. Here is an example of how to achieve this by using DENSE_RANK() to rank the products by their prices:

SELECT ProductName, ListPrice, DENSE_RANK() OVER (ORDER BY ListPrice DESC) as Ranking

FROM Product

JOIN ProductPrice ON Product.ProductID = ProductPrice.ProductID;

In this query, we are joining two tables using the JOIN clause and specifying the join condition based on the product IDs. We have then applied the DENSE_RANK() function to the result set, ordering it in descending order based on the list price column. Example 1:

ProductName ListPrice Ranking

————————————

Red Jeans 60.00 1

Black Pants 50.00 2

Pink Dress 45.50 3

White Skirt 35.99 4

Blue T-shirt 25.00 5

Red Shirt 20.00 6

Green Cap 10.00 7

Example 2:

As another example, imagine that you are a manager at a retail store. You want to know which products are selling well in each category, and so you want to rank the products within each category separately.

In this case, you can use DENSE_RANK() over partitions to get the rankings for each category. Here is an example of how to achieve this by using DENSE_RANK() to rank the products by category ID and list price:

SELECT ProductName, ListPrice, CategoryID,

DENSE_RANK() OVER (PARTITION BY CategoryID ORDER BY ListPrice DESC) as Ranking

FROM Products;

In this query, we have used the PARTITION BY clause to identify the range of values, CategoryID, within which DENSE_RANK() will rank the values based on their order, ListPrice. The output shows the result set with the products ranked within each category based on their list price.

Example 1:

ProductName ListPrice CategoryID Ranking

————————————————

Blue T-shirt 25.00 1 1

Red Shirt 20.00 1 2

Green Cap 10.00 1 3

Pink Dress 45.50 2 1

White Skirt 35.99 2 2

Black Pants 50.00 3 1

Red Jeans 60.00 3 2

Example 2:

Suppose you want to know which products are selling well in each category and want to narrow down the results by showing only the top two products in each category. In this case, we can modify the previous query to add another condition after the ranking:

SELECT ProductName, ListPrice, CategoryID,

DENSE_RANK() OVER (PARTITION BY CategoryID ORDER BY ListPrice DESC) as Ranking

FROM Products

WHERE Ranking <= 2;

Here, we have introduced a WHERE clause to limit the output to only show products in the top 2 ranks within each category. The output will be:

ProductName ListPrice CategoryID Ranking

————————————————

Blue T-shirt 25.00 1 1

Red Shirt 20.00 1 2

Pink Dress 45.50 2 1

White Skirt 35.99 2 2

Black Pants 50.00 3 1

Red Jeans 60.00 3 2

Conclusion:

In this article, we have explored advanced examples of the DENSE_RANK() function in SQL Server. We looked at how it can be applied to more complex scenarios, such as ranking products within a result set and using partitions to rank products by different categories.

The DENSE_RANK() function is a powerful tool that can assist in ranking data in a range of different contexts, making it an essential skill for any database user or developer. In summary, this article has explored the SQL Server DENSE_RANK() function with a focus on advanced examples.

We learned about how to use DENSE_RANK() over a result set and partitions to group and rank data in complex scenarios. The DENSE_RANK() function is a valuable tool for ranking values within a specified range and can aid in making data-driven decisions.

By understanding the syntax and parameters of DENSE_RANK(), readers can effectively apply this function to rank values in their databases. In conclusion, DENSE_RANK() is an essential skill for any database user or developer who wants to effectively use SQL Server.

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