📌 SFMC Data Extensions (DE) - Interview Q&A

Master Data Extensions in **Salesforce Marketing Cloud (SFMC)** with this in-depth Q&A guide for interviews.

📌 Table of Contents

• 1️⃣ Basics of Data Extensions
• 2️⃣ Structure & Fields in DEs
• 3️⃣ Data Relationships & Querying
• 4️⃣ Managing & Automating Data
• 5️⃣ Best Practices
• 6️⃣ Troubleshooting & Integration

1️⃣ Basics of Data Extensions

Q1: What is a Data Extension (DE) in SFMC?

A: A Data Extension is a **relational database table** in SFMC that stores subscriber data, transactional data, and custom fields.

Q2: What are the different types of Data Extensions?

• ✔ Sendable DE: Used for sending emails or SMS.
• ✔ Non-Sendable DE: Stores metadata or lookup data.

2️⃣ Structure & Fields in DEs

Q3: What are the key components of a Data Extension?

• 📌 Name: Identifier for the DE.
• 📌 Fields: Columns storing data (e.g., Email, First Name).
• 📌 Primary Key: Ensures uniqueness of records.
• 📌 Retention Policy: Auto-deletes data after a period.

3️⃣ Data Relationships & Querying

Q4: How can Data Extensions be related to each other?

A: DEs use "Primary Key – Foreign Key" relationships like relational databases.

Q5: How do you retrieve data using SQL in SFMC?

SELECT s.EmailAddress, s.FirstName, o.EventDate  
FROM _Subscribers s  
INNER JOIN _Open o  
ON s.SubscriberKey = o.SubscriberKey;
            

4️⃣ Managing & Automating Data

Q6: How can you import data into a Data Extension?

• ✔ Manual Upload via Import Wizard.
• ✔ Automation Studio – File Import Activity.
• ✔ API Integration – REST/SOAP APIs.

Q7: How do you automate DE updates?

Using Automation Studio:

• ✅ **SQL Query Activity** – Update DEs.
• ✅ **File Import Activity** – Scheduled imports.
• ✅ **FTP Integration** – Automate CSV uploads.

5️⃣ Best Practices

Q8: What are best practices for Data Extensions?

• ✔ Use **Indexed Fields** for faster queries.
• ✔ Avoid `SELECT *` in SQL Queries.
• ✔ Enable **Retention Policies** to auto-clean data.
• ✔ Use **Primary Keys** to prevent duplicates.

6️⃣ Troubleshooting & Integration

Q9: How do you troubleshoot Data Extension issues?

• ✔ Check for **duplicate records**.
• ✔ Validate **data types** (wrong formats cause errors).
• ✔ Monitor **SQL Query Logs** in Automation Studio.

🚀 Ready to Master SFMC Data Extensions?

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