DENSE_RANK

Purpose: DENSE_RANK computes the rank of a row in an ordered group of rows and returns the
rank as a NUMBER. The ranks are consecutive integers beginning with 1. The largest
rank value is the number of unique values returned by the query. Rank values are not
skipped in the event of ties. Rows with equal values for the ranking criteria receive the
same rank. This function is useful for top-N and bottom-N reporting.
This function accepts as arguments any numeric datatype and returns NUMBER.

As an aggregate function, DENSE_RANK calculates the dense rank of a hypothetical
row identified by the arguments of the function with respect to a given sort
specification. The arguments of the function must all evaluate to constant
expressions within each aggregate group, because they identify a single row
within each group. The constant argument expressions and the expressions in the
order_by_clause of the aggregate match by position. Therefore, the number of
arguments must be the same and types must be compatible.
■ As an analytic function, DENSE_RANK computes the rank of each row returned
from a query with respect to the other rows, based on the values of the value_
exprs in the order_by_clause.

RANK

Purpose: RANK calculates the rank of a value in a group of values. The return type is NUMBER
Rows with equal values for the ranking criteria receive the same rank. Oracle Database
then adds the number of tied rows to the tied rank to calculate the next rank.
Therefore, the ranks may not be consecutive numbers. This function is useful for top-N
and bottom-N reporting.