More about the uncorrelated case: I don't believe there should be any attempt to coordinate executions. For example,
SELECT a FROM t1
UNION ALL
SELECT a FROM t2
t1 and t2 can be executed entirely independently with no need for results to be delayed to the client.
More about the uncorrelated case: I don't believe there should be any attempt to coordinate executions. For example,
SELECT a FROM t1
UNION ALL
SELECT a FROM t2
t1 and t2 can be executed entirely independently with no need for results to be delayed to the client.