Handling duplicate data is a significant challenge that data engineers encounter regularly. In the DP-203 Data Engineering on Microsoft Azure exam, understanding how to tackle this issue is important. In this post, we delve into the strategies of managing and resolving duplicate data in Azure.
Understanding Duplicate Data
Duplicate data occurs when records in a dataset repeated unnecessarily. This can lead to skewed analysis, incorrect insights, increased resource consumption, and reduced system performance. Therefore, identifying and rectifying duplicate data is essential.
Dealing with Duplicate Data in Azure
On the Microsoft Azure platform, different data services can help identify and eliminate duplicate data. One such service is Azure Data Factory, a cloud-based data integration service.
Azure Data Factory allows data engineers to create data-driven workflows for ingestion, transformation, and integration of data. Using the ‘Copy Data’ component, it’s possible to delete duplicate rows in the dataset.
#Let's consider a sample customer data in Azure Data Factory
customerData = spark.read.format("csv").load("adftutorial/input/customer.csv")
customerData.show(5)
#Let's identify the duplicates in the customer data
duplicates = customerData.groupBy("CustomerId").count().where("`count` > 1")
duplicates.show(5)
#Let's remove the duplicates
customerDataDistinct = customerData.dropDuplicates()
customerDataDistinct.show(5)
In the code snippet above, a customer dataset is read in Azure Data Factory, duplicates are identified, and then dropped.
Using Azure Data Lake Analytics
Another service that can be used to handle duplicate data is Azure Data Lake Analytics. It is an on-demand analytics job service that simplifies big data. With U-SQL, a language that combines the power of SQL with the extensibility of C#, it is possible to analyze and reduce large and complex data.
Here is the U-SQL script to remove duplicates in Azure Data Lake Analytics:
@input_data =
EXTRACT date string,
time string,
s_sitename string,
cs_method string,
csuristem string
FROM "/SearchLog.tsv"
USING Extractors.Tsv();
@result =
SELECT DISTINCT *
FROM @input_data;
OUTPUT @result
TO "/SearchLog-distinct.tsv"
USING Outputters.Tsv();
This script extracts data from the SearchLog.tsv file, removes duplicates using the SELECT DISTINCT statement, and outputs the distinct records to SearchLog-distinct.tsv.
Utilizing Azure Databricks
Azure Databricks is another powerful tool that provides an interactive workspace for data exploration, cleaning, and transformation. It comes with a dynamic in-memory based Spark cluster service.
Duplicate data in dataframes can be easily identified and removed using functions like dropDuplicates() or distinct().
# Loads data.
df = spark.read.format("json").load("/databricks-datasets/structured-streaming/events/file-0.json")
df.show(5)
# Count before removing duplicates
print(df.count())
# Removes duplicates.
df = df.dropDuplicates()
# Count after removing duplicates
print(df.count())
In the above snippet, the dataframe is loaded from a JSON file. The count before and after removing duplicates is printed which indicates the number of duplicates that were present in the original dataframe.
From the discussions above, you can see why handling duplicate data is an essential skill for anyone preparing for the DP-203 Data Engineering on Microsoft Azure exam. Understanding how to handle duplicate data in Azure Data Factory, Azure Data Lake Analytics, and Azure Databricks, can help you get closer to acing this exam.
Practice Test
True/False: Azure Data Factory does not have any built-in methods to handle duplicates in data streams.
- Answer: False
Explanation: Azure Data Factory provides steps such as the ‘Remove Duplicates’ transformation in data flow which can be used to handle duplicate data.
In Azure Synapse Analytics, which function helps in deleting duplicates?
- a) REMOVE DUPLICATES
- b) DELETE DUPLICATE
- c) DEDUCE DUPLICATES
- d) DISTINCT
Answer: d) DISTINCT
Explanation: The DISTINCT function in Azure Synapse Analytics is used to delete duplicate rows in a column or in a table.
Multiple Select: Which of the following tools in Azure can help in handling duplicate data?
- a) Azure Data Factory
- b) Azure Synapse Analytics
- c) Azure Machine Learning
- d) Azure Cosmos DB
Answer: a) Azure Data Factory, b) Azure Synapse Analytics
Explanation: Both Azure Data Factory and Azure Synapse Analytics have built-in ways to handle and remove duplicate data.
True/False: DISTINCT in SQL can only be used with single column.
- Answer: False
Explanation: DISTINCT can be used with one or more columns of a table. When used with multiple columns, it considers the uniqueness of rows based on the combination of all specified column values.
True/False: Azure Data Factory can remove duplicates from data streams in real-time.
- Answer: False
Explanation: Azure Data Factory is a batch processing service and cannot handle duplicates in real-time.
In Azure Data Factory, what happens if the ‘Allow duplicates’ option in the ‘Union’ transformation is not checked?
- a) It removes all duplicate rows.
- b) It keeps all duplicate rows.
- c) It generates an error.
- d) It automatically checks the ‘Allow duplicates’ option.
Answer: a) It removes all duplicate rows.
Explanation: The ‘Allow duplicates’ option in the ‘Union’ transformation keeps all duplicate rows when checked; if it is not checked, the transformation removes all duplicate rows.
True/False: Azure Stream Analytics has built-in functionality to handle duplicates emerging from stream input or data drift.
- Answer: True
Explanation: Azure Stream Analytics provides event ordering and duplicate detection for data streams.
Multiple select: Which of the following can potentially cause duplicate data in your Azure data storage?
- a) Data drift
- b) Faulty data pipelines
- c) Insufficient storage capacity
- d) Concurrent writes
Answer: a) Data drift, b) Faulty data pipelines, d) Concurrent writes
Explanation: Data drift, faulty pipelines, and concurrent writes are all potential causes of duplicate data. Insufficient storage capacity does not cause data duplication.
True/False: Using Partitioning in Azure Table Storage can prevent data duplication issues.
- Answer: False
Explanation: While partitioning helps with scaling and performance, it does not have a built-in mechanism for preventing data duplication.
In Azure Data Explorer, how can you remove duplicate records in the data ingestion process?
- a) Use the .ingest inline command with the ‘dropBy’ clause.
- b) Use the .delete replica command.
- c) Use the .ingest truncate command.
- d) None of above.
Answer: a) Use the .ingest inline command with the ‘dropBy’ clause.
Explanation: The ‘dropBy’ clause in the .ingest inline command allows us to specify one or more columns to determine duplicates during data ingestion process in Azure Data Explorer.
Interview Questions
What is the importance of addressing duplicate data in the context of DP-203 Data Engineering on Microsoft Azure?
Duplicate data poses several problems, including skewed data analytics, misleading statistical results, and increased storage costs. Eliminating them helps ensure accurate analytics and reduces storage costs on Azure.
What Azure tool can be used to handle and clean duplicate data?
The Azure Data Factory can be used. It has a data flow transformation called Deduplicate that removes duplicate rows in the data.
What is the role of the Azure Data Factory’s Deduplicate transformation in handling duplicate data?
Deduplicate Transformation in Azure Data Factory is used to remove duplicate rows based on certain columns selected. The remaining unique rows are then outputted for further processing.
What is the general working principle of the Azure Data Factory’s Deduplicate function?
It works by comparing the rows of data within a distinct set of columns. If this set of columns has duplicate rows, the function would keep only a single row and remove the remaining duplicates.
Can Azure Databricks be used to handle duplicate data?
Yes, Azure Databricks is a big data analytics platform that can identify and eliminate duplicate data.
What attributes can be used as criteria for identifying duplicate data in Azure Data Factory’s Deduplicate transformation?
Any column or set of columns can be used as criteria for identifying duplicate data in Azure Data Factory’s Deduplicate transformation.
How can we avoid generating duplicate data during data ingestion in Azure?
Implementing good data validation checks during the data ingestion phase can help avoid the entry of duplicate data. Also, functions like Deduplicate in Azure Data Factory can be used to cleanse the data.
What is a primary key and how can it help handle duplicate data?
A primary key uniquely identifies each record in a database table. Ensuring that each record has a unique primary key can prevent the insertion of duplicate records.
How can Azure Data Explorer help in handling duplicate data?
Azure Data Explorer has built-in functions like the .ingest inline command, which prevents duplication by checking whether records with the same exact properties already exist before inserting new ones.
Does Azure SQL Database have any features to deal with duplicate data?
Yes. Azure SQL Database can use primary keys and unique constraints to prevent the insertion of duplicate records. Also, T-SQL commands like “SELECT DISTINCT” can be used to handle duplicate data in Azure SQL Database.
How does Azure Synapse Analytics handle duplicate data?
Azure Synapse supports T-SQL, which can be used along with primary keys and unique constraints to prevent the creation of duplicate records. Standard commands like “SELECT DISTINCT” can also be used to eliminate duplicate rows.
How does Azure Logic Apps handle duplicate data?
Azure Logic Apps can make use of the “Select” action to identify and remove duplicates from the dataset based on certain criteria.
Which Azure data storage service provides automatic deduplication capabilities?
Azure Data Lake Store has an automatic deduplication feature, which can be enabled to prevent the storage of duplicate data.
How does the Azure Data Factory’s Deduplicate function determine which of the duplicate rows to keep?
The Deduplicate function keeps the first row by default, based on the natural order of the data. However, this behavior can be customized.
Can Azure Machine Learning be utilized to handle duplicate data?
Yes. Azure Machine Learning provides data preparation options that include removing exact duplicate rows based on all columns.
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