Use functional dependencies to optimize unnecessary order key column

[kwannoel]

The query:

create table t1(id bigint primary key, i bigint);
create materialized view mv1 as select id, i from t1 order by id, i;

Has the plan:

 StreamMaterialize {
   columns: [id, i],
   stream_key: [id],
   pk_columns: [id, i],
   pk_conflict: NoCheck 
 }
 └─StreamTableScan { table: t1, columns: [id, i] }

But there's a functional dependency because id is the stream key:

id -> i

So this means we won't have such cases:

id	i
1	2
1	3

This means in the sql above, we actually just need to have id as the pk columns, since i won't affect the sorting:

 StreamMaterialize {
   columns: [id, i],
   stream_key: [id],
   pk_columns: [id],
   pk_conflict: NoCheck 
 }
 └─StreamTableScan { table: t1, columns: [id, i] }

Specifically, in cases where there is a functional dependency between the prefix and the next column, we can prune the next column.