Описание тега dense-rank
dense_rank() is a window, or analytic, function, which computes the rank of each row in a query, within a partition of a result-set and based on the values in the ORDER BY clause. Unlike rank() there will never be any gaps in the ranking.
For SQL Server
Returns the rank of rows within the partition of a result set, without any gaps in the ranking. The rank of a row is one plus the number of distinct ranks that come before the row in question.
For Oracle
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.
Questions tagged dense-rank should also be tagged with the appropriate RDBMS, for instance sql-server or oracle and, if appropriate, the specific version.