Oracle Merge Statement

MERGE Statement
The MERGE statement can be used to conditionally insert or update data depending on its presence.
This method reduces table scans and can perform the operation in parallel. Consider the following example where data from the HR_RECORDS table is merged into the EMPLOYEES table.

MERGE INTO employees e USING hr_records h ON (e.id = h.emp_id) WHEN MATCHED THEN UPDATE SET e.address = h.address WHEN NOT MATCHED THEN INSERT (id, address) VALUES (h.emp_id, h.address);

The source can also be a query.
MERGE INTO employees e USING (SELECT * FROM hr_records WHERE start_date > ADD_MONTHS(SYSDATE, -1)) h ON (e.id = h.emp_id) WHEN MATCHED THEN UPDATE SET e.address = h.address WHEN NOT MATCHED THEN INSERT (id, address) VALUES (h.emp_id, h.address);

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