•Idea: for each subset
of {R1, …, Rn}, compute the best plan
for that subset
•In increasing
order of set cardinality:
–Step 1: for
{R1}, {R2}, …, {Rn}
–Step 2: for
{R1,R2}, {R1,R3}, …, {Rn-1, Rn}
–…
–Step n: for
{R1, …, Rn}
•A subset of
{R1, …, Rn} is also called a subquery