The MERGE command (also known as UPSERT) is used to write data into a Delta table while avoiding duplicate records. It allows you to:
- Update existing records when a match is found
- Insert new records when no match is found
- Delete records when specified conditions are met
This is particularly useful for:
- Incremental data processing where you need to update existing records
- Data deduplication scenarios
- Slowly Changing Dimensions (SCD) implementations
Other options:
- DROP: Deletes the entire table
- INSERT: Adds new records but doesn't prevent duplicates
- APPEND: Adds data to the end of the table without checking for duplicates
The MERGE command uses a source table/view and a target table, and performs conditional updates/inserts based on matching criteria, making it ideal for avoiding duplicate records.
