Upsert is a composite term made up of “insert” and “update”, broadly used within database management systems that refer to a smart operation capable of determining whether to insert or update an entry on execution. In the context of Data engineering on Microsoft Azure, specifically for the DP-203 Data Engineering, understanding and leveraging the Upsert operation is essential.
The Upsert function can be used for both structured and unstructured data, making it a versatile resource. It ensures there is no duplication of data records and maintains the integrity and accuracy of the database. It further plays a crucial role in ETL (Extract, Transform, Load) processes.
Usage of Upsert in Azure Cosmos DB
Azure Cosmos DB is a hugely popular NoSQL database offering from Microsoft Azure. It is globally distributed and supports the use of Upsert for data management. Upsert is particularly useful in Cosmos DB where you have a large volume of data entries and needs to maintain an efficient way of updating existing records or inserting new ones.
Below is an example of how to use Upsert in Azure Cosmos DB with .Net SDK:
DocumentClient upsertClient = new DocumentClient(new Uri(“endpoint”), “authKey”);
dynamic upsertDocument = new {
id = “someId”,
category = “Some category”,
_rid = “someRid”,
_self = “someSelf”,
_ts = 140,
_etag = “someEtag”
};
var upsertResponse = await upsertClient.UpsertDocumentAsync(“collectionLink”, upsertDocument);
dynamic savedDocument = upsertResponse.Resource;
In the above code, the upsert operation is performed on a document with a specified ‘id’. If a document with the same ‘id’ exists, then it will be updated; if it doesn’t exist, then a new document will be inserted.
Usage of Upsert in Azure Data Lake Store
In Azure Data Lake Store, the Upsert function is beneficial when dealing with big data analytics workloads. To illustrate this, let’s consider an example where you have to update or merge a large dataset stored in Azure Data Lake Store.
In this scenario, you can first dump all the raw data into the Azure Data Lake Storage and then use U-SQL scripts to transform this raw data into a more significant format. The upsert logic can be implemented using a combination of U-SQL’s JOIN, SELECT EXCEPT, and UNION ALL statements.
Here’s an example of how to perform an upsert operation in Azure Data Lake Store using U-SQL:
@delta = SELECT * FROM (VALUES
(“john”, “doe”, “manager”),
(“mary”, “smith”, “engineer”)) AS
D(firstname, lastname, profession);
@existing = SELECT * FROM (VALUES
(“john”, “brown”, “developer”),
(“mary”, “smith”, “analyst”)) AS
E(firstname, lastname, profession);
@merged =
SELECT lastname, firstname, profession FROM @delta
UNION ALL
SELECT E.lastname, E.firstname, E.profession
FROM @existing AS E
LEFT JOIN @delta AS D
ON E.lastname == D.lastname AND E.firstname == D.firstname
WHERE D.lastname == null;
OUTPUT @merged
TO “/output/upsert.csv”
USING Outputters.Csv();
From this, it is evident that understanding the Upsert operation, its utilization in Azure frameworks is crucial for the DP-203 Data Engineering. Utilizing Upsert operations in data engineering processes can save significant computing resources, minimize redundancy, maintain data integrity and increase overall efficiency.
Practice Test
What operation is performed by Azure Synapse Analytics to perform upserts in data streams?
- A. MERGE
- B. SPLICE
- C. MASK
- D. MODIFY
Answer: A. MERGE
Explanation: The MERGE operation is a combination of the UPDATE and INSERT operations, and is often used in a data upsert context.
True or False: Upsert method is a combination of UPDATE and DELETE operations?
Answer: False.
Explanation: Upsert method is a combination of UPDATE and INSERT operations. If the data already exists in the database, it is updated; if not, it is inserted.
Azure Stream Analytics supports which operation for upserts in the reference data?
- A. DELETE
- B. TRUNCATE
- C. REPEAT
- D. None of the above
Answer: D. None of the above.
Explanation: Azure Stream Analytics does not support the upsert operation for reference data.
In SQL Server, which operation can be used to perform upserts?
- A. DELETE
- B. INSERT…ON DUPLICATE KEY UPDATE
- C. MERGE
- D. Both B and C
Answer: D. Both B and C.
Explanation: In SQL Server, the operation that can be used to perform upserts are INSERT…ON DUPLICATE KEY UPDATE and MERGE.
What is upsert in data management?
- A. It is a process where only new data is inserted.
- B. It is a process where data is updated only if it exists.
- C. It is a process where data is inserted if it doesn’t exist, and updated if it exists.
- D. None of the above
Answer: C. It is a process where data is inserted if it doesn’t exist, and updated if it exists.
Explanation: In data management, upsert is a combination of INSERT and UPDATE operations. When new data is added, it’s first checked if it already exists. If it does, the data is updated. If not, it’s inserted as a new record.
True or False: Upsert operations are only supported by SQL-based databases and not by NoSQL databases.
Answer: False.
Explanation: Most of the modern SQL and NoSQL databases support upsert operations.
What does an upsert operation do if a record exists?
- A. Deletes it
- B. Ignores it
- C. Updates it
- D. None of the above
Answer: C. Updates it.
Explanation: An Upsert operation update the record if it exists.
What happens during an upsert operation if a record does not exist?
- A. It is deleted
- B. It is ignored
- C. It is inserted
- D. None of the above
Answer: C. It is inserted.
Explanation: During an Upsert operation, if the record does not exist, it is inserted.
Which feature in Azure Storage Explorer helps to import and export data in Azure Cosmos DB more efficiently?
- A. Blob Storage
- B. Azure Functions.
- C. Bulk Executor
- D. Azure Active Directory
Answer: C. Bulk Executor
Explanation: The Bulk Executor feature in Azure Cosmos DB’s SDKs allows importing and exporting large quantities of data more efficiently. It provides functionality for bulk operations including Upsert.
True/False: Optimistic concurrency controls help prevent conflicts during Upsert operations.
Answer: True
Explanation: Optimistic concurrency controls can be utilized to avoid conflicts during Upsert operations by ensuring that updates and deletes are made to the correct version of a row or document.
Interview Questions
What does the term ‘upsert’ mean in data engineering?
Upsert is a smart operation which is a combination of UPDATE and INSERT. It inserts rows that don’t exist and updates the rows that do exist.
How can you perform an upsert operation in Azure Cosmos DB?
To perform an upsert in Azure Cosmos DB, you can use the Upsert API. You pass in the document with the changes, if the document exists it will be updated; if it does not, it will be created.
Which storage systems in Azure support upsert operation?
Azure table storage and Azure Cosmos DB are the storage systems in Azure that support upsert operations.
How do you use the MERGE statement to achieve upsert functionality in Azure SQL Database?
The MERGE statement in Azure SQL Database is used to perform operations that synchronize two tables by inserting, updating, or deleting rows. For upsert functionality, the MERGE statement attempts to update the record, and if it does not exist, it will insert a new record.
Which DML operation is used to perform upsert in Azure Cosmos DB?
In Azure Cosmos DB, upsert operation is performed with “Upsert” DML operation.
In Azure Data Factory, which activity can be used to perform upsert operations?
In Azure Data Factory, upsert operations can be performed using the Copy activity with ‘Allow upsert’ option.
Does Apache Cassandra API for Azure Cosmos DB support upsert operation?
Yes, Apache Cassandra API for Azure Cosmos DB supports upsert operation.
Can Azure Stream Analytics perform upsert operations?
Yes, Azure Stream Analytics has the ability to perform upsert operations to Azure SQL Database, Azure Cosmos DB and Power BI.
Is the Upsert operation in Azure Cosmos DB case-sensitive?
Yes, the Upsert operation in Azure Cosmos DB is case-sensitive.
In terms of performance, how does an upsert operation compare to separate insert and update operations?
An upsert operation is generally more efficient than separate insert and update operations as it entails only a single read-write operation.
How can you achieve Upsert functionality in Azure Table Storage?
In Azure Table Storage, the ‘InsertOrReplace’ or ‘InsertOrMerge’ operations can be used to achieve upsert functionality.
Why would you use an upsert operation instead of separate insert and update operations in Azure SQL Database?
Using an upsert operation simplifies code logic as it removes the need to differentiate between a new row or an existing row. It is also more efficient in terms of performance as it entails only a single read-write operation.
What is the key prerequisite for using upsert in Azure Cosmos DB?
The key prerequisite for using upsert in Azure Cosmos DB is that the document must have an id property that is used to identify if a document with the same id already exists.
Does Upsert operation replace the entire document in Azure Cosmos DB?
Yes, the Upsert operation replaces the entire document if the document with same id already exists in Azure Cosmos DB.
Can upsert operations in Azure lead to any type of data loss?
If not handled properly, upsert operations could lead to data loss in instances where an existing item is fully replaced by a new item especially in Azure Cosmos DB where upsert replaces the entire document.
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