Databricks Certified Data Engineer - Associate

The MERGE command (also known as UPSERT) is specifically designed to write data into a Delta table while avoiding duplicate records. It performs the following operations:

1. WHEN MATCHED: Updates existing records when a match is found
2. WHEN NOT MATCHED: Inserts new records when no match is found

This allows you to:

• Update existing records with new values
• Insert new records that don't already exist
• Skip or handle duplicates based on specified conditions

Other options:

• DROP: Deletes a table entirely
• INSERT: Simply inserts data without checking for duplicates
• APPEND: Appends data to a table without checking for duplicates

The MERGE command is essential for maintaining data integrity and preventing duplicate records in Delta tables.