Working with Redshift NTILE Window Function: Made Easy 101

on Amazon Redshift, Data Warehouses, Redshift Commands, Redshift Functions, Tutorials • January 24th, 2022 • Write for Hevo

Amazon Redshift is a petabyte-scale Cloud-based Data Warehouse service. It is optimized for datasets ranging from a hundred gigabytes to a petabyte can effectively analyze all your data by allowing you to leverage its seamless integration support for Business Intelligence tools.

Window functions are used to perform analytic business queries more efficiently. To be specific, they help you perform queries on a particular group of data in a dataset. These data sets are usually result sets in an existing window. That’s exactly where window functions operate – in an existing window. The Redshift NTILE window function is one of the several window functions available for use on Amazon Redshift.

In this article, you will gain information about Redshift NTILE Window Functions. You will also gain a holistic understanding of Amazon Redshift, its key features, types Window Functions, and the different uses of Amazon Redshift NTILE Window Functions. Read along to find out in-depth information about Amazon Redshift NTILE Window Functions.

Table of Contents

What is Amazon Redshift?

Redshift NTILE Window Function - Redshift Logo| Hevo Data
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Amazon Web Services (AWS) is a subsidiary of Amazon saddled with the responsibility of providing a cloud computing platform and APIs to individuals, corporations, and enterprises. AWS offers high computing power, efficient content delivery, database storage with increased flexibility, scalability, reliability, and relatively inexpensive cloud computing services.

Amazon Redshift, a part of AWS, is a Cloud-based Data Warehouse service designed by Amazon to handle large data and make it easy to discover new insights from them. Its operations enable you to query and combine exabytes of structured and semi-structured data across various Data Warehouses, Operational Databases, and Data Lakes.

Amazon Redshift is built on industry-standard SQL with functionalities to manage large datasets, support high-performance analysis, provide reports, and perform large-scaled database migrations. Amazon Redshift also lets you save queried results to your S3 Data Lake using open formats like Apache Parquet from which additional analysis can be done on your data from other Amazon Web Services such as EMR, Athena, and SageMaker.

For further information on Amazon Redshift, you can follow the Official Documentation.

Key Features of Amazon Redshift

The key features of Amazon Redshift are as follows:

1) Massively Parallel Processing (MPP)

Massively Parallel Processing (MPP) is a distributed design approach in which the divide and conquer strategy is applied by several processors to large data jobs. A large processing job is broken down into smaller jobs which are then distributed among a cluster of Compute Nodes. These Nodes perform their computations parallelly rather than sequentially. As a result, there is a considerable reduction in the amount of time Redshift requires to complete a single, massive job.

2) Fault Tolerance

Data Accessibility and Reliability are of paramount importance for any user of a database or a Data Warehouse. Amazon Redshift monitors its Clusters and Nodes around the clock. When any Node or Cluster fails, Amazon Redshift automatically replicates all data to healthy Nodes or Clusters.

3) Redshift ML

Amazon Redshift houses a functionality called Redshift ML that gives data analysts and database developers the ability to create, train and deploy Amazon SageMaker models using SQL seamlessly.

4) Column-Oriented Design

Amazon Redshift is a Column-oriented Data Warehouse. This makes it a simple and cost-effective solution for businesses to analyze all their data using their existing Business Intelligence tools. Amazon Redshift achieves optimum query performance and efficient storage by leveraging Massively Parallel Processing (MPP), Columnar Data Storage, along with efficient and targeted Data Compression Encoding schemes.

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What are Window Functions in Amazon Redshift?

Window Functions enable analytic business queries in a better and efficient manner. They are used to derive Point-Blank insights from a result set without external input. In addition to that, they are used based on the current need and their input can be modified syntactically.

Usage Of Window Functions

Several uses of Window Functions include:

  • They are used to perform queries on a group of data in a dataset.
  • They are used to output results without manipulating the output of the result set.
  • They are used to access the detail of the rows from an aggregation.

The functions stated above are an encapsulation of the practical results derived from different Window Functions. This leads us to the types of window functions and their examples.

Types Of Redshift Window Functions

Diffferent types of Window Functions Amazon Redshift supports are as follows:

1) Aggregate Window Functions

Aggregate Window Functions operate like the traditional aggregate functions in SQL operating Data Warehouses. They return a single value from a group of rows derived from a result set.

The examples include:

  • SUM()
  • MAX()
  • MIN()
  • AVG()

The functions given above will return a single value.

2) Ranking Window Functions

Ranking Window functions return the rank of a specific record based on based on the ORDER BY expression in the OVER clause. 

Examples of Ranking Wndow Functions are:

  • RANK()
  • DENSE_RANK()
  • NTILE()

3) Value Window Functions

Value Window Functions return a certain value based on a certain criteria given.

Examples of Value Window Functions include:

  • LAG()
  • LEAD()
  • FIRST_VALUE()

What is Redshift NTILE Window Function?

Redshift NTILE: Redshift NTILE Window Function| Hevo Data
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The Redshift NTILE function is used to distribute rows of an ordered partition into a specified number of groups. It divides ordered rows in the partition into a specified number of ranked groups. The groups are approximately equal to each other and they are numbered in an ordered manner i.e, from number “1”. 

To understand further about Redshift NTILE Window Functions:

1) Syntax

NTILE(expression)
       OVER([PARTITION BY partition_name] [ORDER BY (ASC | DESC)

2) Arguments

The arguments are as follows:

A) Expression

The Expression argument specifies the number of ranking groups. The value must be an integer (i.e greater than 0), and this value cannot be nullable. At no point in the analysis with the value of an expression be empty.

B) OVER

The OVER statement is the clause that specifies the window partitioning and ordering of the result set to be queried. It can only contain a partition and not a window frame specification. In practice, it is used alongside the ORDER BY expression.

C) PARTITION BY (optional)

The PARTITION BY statement specifies the window partition to be used i.e the range of records in each group in the OVER clause.

D) ORDER BY (optional)

The ORDER BY expression specifies the ordering of the records in either ascending or descending order. If it is omitted, the ranking behavior will remain the same.

The OVER expression holds the information about the partition to be queried and the order in which the result set should be rendered. 

Sample Usage: Redshift NTILE function

The Redshift NTILE function is quite versatile. It can be used in the following variety of ways:

1) Without specifying the Partition Name

The following query showcases the usage of the Redshift NTILE Window function without specifying the partition name.

SELECT month, NTILE(4) 
   OVER( ORDER BY engagements DESC)

The above query would group the results in 4 pairs as specified in the NTILE expression and are ordered in descending order.

2) Specifying the Partition Name 

The following query showcases the usage of Redshift NTILE Window function by specifying the Partition Name.

SELECT product_name, month
     NTILE(4) OVER (PARTITION BY product_name
                    ORDER BY engagements ASC)

The above query would return a data set of the engagements based on the product name in ascending order.

3) Without specifying the Order

The following query showcases the usage of Redshift NTILE Window function without specifying the Order.

SELECT product_name, month
       NTILE(4) OVER (
                      PARTITION BY product_name
                      ORDER BY engagements ASC)

The above query would return a data set of the engagements based on the product name without regard to the order.

4) Specifying the Order

The following query showcases the usage of Redshift NTILE Window function by specifying the Order.

SELECT product_name, month
        NTILE(4) OVER (
                       PARTITION BY product_name
                       ORDER BY engagements DESC)

The above query would return a data set of the engagements based on the product name in descending order.

Professionally, Redshift NTILE functions are very useful for Big Data engineers to get out-of-the-box data and map it to an insight they already have to improve the decision-making of the parent benefactor.

Conclusion

In this article, you have learnt about the Window functions in Amazon Redshift, their uses, and their types. Additionally, you also learnt how to work with the Redshift NTILE functions. Amazon Redshift provides loads of other window functions that are ubiquitous across most Database Management Systems (DBMS) and Data Warehouses that operate primarily on SQL. Their usage depends on your need.

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