Re: Performance improvement for joins where outer side is unique

Hi,

I've been hacking a bit at the join code again... This time I've been putting some effort into  optimising the case where the inner side of the join is known to be unique.

For example, given the tables:

create table t1 (id int primary key);

create table t2 (id int primary key);

And query such as:

select * from t1 left outer join t2 on t1.id=t2.id;

It is possible to deduce at planning time that "for each row in the outer relation, only 0 or 1 rows can exist in the inner relation", (inner being t2)