Your role in this lesson is ENGINEER, which can change the SALES tables.
INSERT INTO t SELECT ... adds the rows a query returns.UPDATE t SET col = ... WHERE ... changes rows. UPDATE t SET ... FROM other WHERE t.id = other.id takes the new values from another table.DELETE FROM t WHERE ... removes rows. Without WHERE, it removes them all.
MERGE combines insert and update, which is how most pipelines load a change feed:
MERGE INTO sales.customers t
USING latest s ON t.customer_id = s.customer_id
WHEN MATCHED THEN UPDATE SET email = s.email
WHEN NOT MATCHED THEN INSERT (customer_id, email) VALUES (s.customer_id, s.email);
If the source has two rows for one key, MERGE can't tell which to apply, so deduplicate the source first, typically with QUALIFY. Each statement returns how many rows it changed.