Hi all,
I'm not sure if this is an appropriate forum, I want to discuss concepts in
the "One SQL to Rule Them All" paper. The paper uses `EMIT STREAM` clause,
but Calcite uses the `STREAM` keyword after `SELECT`, but in my
understanding, these are the same.
I'm wondering about the supposed semantics of the clause with multiple
relations queried. It's supposed to produce a streaming output instead of
instantaneous one. But IMO, you need to specify this property for each
input relation.
Take an example. Let's have ORDER_ITEM and PRODUCT relations.
ORDER_ITEM(product_id, quantity, ...);
PRODUCT(product_id, name);
We want to join these and get a streaming result:
SELECT STREAM * FROM order_item o JOIN product p USING(product_id)
What should this query output? Intuitively, for each change event in
order_item query it should find a matching product and emit that together.
But it could be also interpreted that we treat the product as a
time-varying relation: for each change event in order_item query all
matching changes in product.
I don't see which of the above behaviors should be chosen, provided both
`order_item` and `product` relations can be accessed as point-in-time
relations or time-varying relations.
Regards,
Viliam
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