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SELECT /*+ USE_HASH('Orders', 'Customers') */ o.order_id, o.total, c.country, c.zip
FROM Orders AS o
JOIN Customers FOR SYSTEM_TIME AS OF o.proc_time AS c
ON o.customer_id = c.id;

Note:

1. Table names in use_hash hint is required to avoid mistake hint propagation if there are multiple lookup joins.
2. The hint only provides a suggestion to the optimization, it is not an enforcer.

Proposed Changes

Define Hint Strategy

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So hash lookup Join requires that the input stream should be insert_only stream or it's its upsert keys contains hash keys.

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