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When you choose the Append Unique Rows option, if a row’s unique key already exists in the target table, the incoming row is ignored and the existing row is left unchanged. Only rows with a unique key that doesn’t yet exist in the target are inserted.
Unlike Upsert Row, this mode never modifies existing records; it only inserts new ones.

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Parameters

Merge Columns, Exclude Columns, and On Schema Change don’t apply to this write mode. If you switch to Append Unique Rows from another merge approach, any values set for those options are cleared.

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Example: Append new orders only

An order table uses ORDER_ID as the unique key. The incoming dataset includes a status update for an existing order and one new order.
Existing target table

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Incoming dataset

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Resulting target table

Because ORDER_ID 101 already exists in the target table, its incoming row is ignored, so the existing Shipped status is left unchanged.ORDER_ID 103 doesn’t exist in the target, so it’s inserted as a new row.ORDER_ID 102 has no matching row in the incoming dataset, so it’s left as-is.