Hello, In this query: UPDATE foo SET allocated_to=? WHERE id=(SELECT MIN(id) FROM foo WHERE allocated_to IS NULL) AND allocated_to IS NULL RETURNING id
Is it guaranteed in any way that there will only be one id allocated and returned even if multiple clients are executing this query concurrently? Or is there a possibility that some other client executing this query (or another query modifying allocated_to) might set allocated_to to non-NULL and commit right after the inner select finds it as NULL, so the outer "AND allocated_to IS NULL" will no longer be true, and the outer query will return nothing?
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