⑴Cost The cost assigned to each step 
of the query plan by the CBO. The CBO works by
generating many different execution paths/plans 
for the same query and assigns a cost to each 
and every one. The query plan with the lowest 
cost wins. In the full outer join example,
we can see the total cost for this query is 10.
⑵Card Card is short for Cardinality. It is the 
estimated number of rows that will flow out
of a given query plan step. In the full outer j
oin example, we can see the optimizer expects
there to be 327 rows in EMP and 4 rows in DEPT.
⑶Bytes The size in bytes of the data the CBO 
expects each step of the plan to return.
This is dependent on the number of rows (Card) 
and the estimated width of the rows.