How does the Overwrite Data Action work in the Output Step? – DESelect

In this article, we will explore how the Overwrite Data Action works for a Target Data Extension with the help of some sample data.

When utilizing DESelect Segment to store Selection results in Target Data Extensions, you have three key Data Actions at your disposal: Overwrite, Append, and Update. In this article, we will delve into the Overwrite Data Action, its functionality, and how it impacts your Target Data Extensions within SFMC. Understanding these Data Actions will help you effectively manage and manipulate data to optimize your marketing campaigns.

Overwrite Data Action: The Overwrite Data Action removes existing records from the Target Data Extension and adds new ones during each Selection run. Unlike other Data Actions, Overwrite does not require Primary Keys. However, if Primary Keys are present, SFMC automatically removes duplicate records randomly. Consider the following example.

Before running the Selection, let's assume the Target Data Extension contains the following data:

Customer ID	First Name	Last Name	Email	Language
C-100	Jane	Jones	jjones1955@hotmail.com	English
C-101	Kofi	Abimbola	kofi1234@gmail.com	Dutch
C-102	Paul	Chang	paul.chang@yahoo.com	English
C-103	Maria	Juarez	MariaJuarez@outlook.com	Spanish

Sample Selection results

Customer ID	First Name	Last Name	Email	Language
C-102	Paul	Chang	paul.chang@yahoo.com	English
C-104	Marie	Benoit	m.benoit@gmail.com	French
C-112	Bjorn	Svenson	b.svenson@yahoo.com	Swedish
C-100	Jane	Jones	jjones1955@hotmail.com	English
C-102	Paul	Chang	paul.chang2@yahoo.com	Chinese

If there’s no Primary Key set, after running the Selection, the updated Target Data Extension will contain the following data: the data in the Target Data Extension will match the results generated.

Customer ID	First Name	Last Name	Email	Language
C-102	Paul	Chang	paul.chang@yahoo.com	English
C-104	Marie	Benoit	m.benoit@gmail.com	French
C-112	Bjorn	Svenson	b.svenson@yahoo.com	Swedish
C-100	Jane	Jones	jjones1955@hotmail.com	English
C-102	Paul	Chang	paul.chang2@yahoo.com	Chinese

If there’s a Primary Key set, after running the Selection, the updated Target Data Extension will contain the following data (with Primary Key Customer ID): the data in the Target Data Extension will be in the order of the results. When a record with a duplicate Primary Key is encountered, it will just get skipped.

Customer ID [PK]	First Name	Last Name	Email	Language
C-102	Paul	Chang	paul.chang@yahoo.com	English
C-104	Marie	Benoit	m.benoit@gmail.com	French
C-112	Bjorn	Svenson	b.svenson@yahoo.com	Swedish
C-100	Jane	Jones	jjones1955@hotmail.com	English

Conclusion: DESelect Segment offers powerful Data Actions—Overwrite, Append, and Update—to manage Target Data Extensions in SFMC efficiently. Understanding the behavior of each action helps ensure accurate and streamlined data operations within your marketing campaigns.

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