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:
- WHEN MATCHED: Updates existing records when a match is found
- 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.
