optimizer: Improve stream key derivation for stream join

[fuyufjh]

If one side is N-to-1 mapping (such as joining a dimension table with its PK), then both the join key and stream key from that side does not need to be included in output stream key.

For example:

Assuming

PK of orders = [order.id]
PK of customers = [customer.id]

Then for this query

select * from orders left join customers on orders.custumer_id = customers.id

Because orders.custumer_id = customers.id is an N-to-1 mapping (from left to right), the Join's (output) stream key can be [orders.id], instead of [orders.id, customers.id] or [orders.id, customers.id, orders.custumer_id].

[fuyufjh]

Thanks to @st1page for the correction, I was wrong. The join key must be included the stream key under any circumstance.

Taking fact table-dimension table join as an example

select * from orders left join customers on orders.customer_id = customers.id

If orders.customer_id is updated, it would generate a pair of U- and U+, which then becomes - and + and sent to 2 actors of the next fragment, saying, a Materialize.

Only by including the customer_id in the stream key can it prevent the + from arriving at Materialize before -, causing a sanity check panic.