Ranking functions let you compile a list of values from the data set in ranked order, as well as compose single-statement SQL queries that fulfil requests such as, “Name the top 10 products shipped this year by total sales,” or “Give the top 5% of salespersons who sold orders to at least 15 different companies.”
SQL/OLAP defines five functions that are categorized as ranking functions:
<RANK FUNCTION TYPE> ::= RANK | DENSE_RANK | PERCENT_RANK | ROW_NUMBER | NTILE
Ranking functions let you compute a rank value for each row in a result set based on the order specified in the query. For example, a sales manager might need to identify the top or bottom sales people in the company, the highest- or lowest-performing sales region, or the best- or worst-selling products. Ranking functions can provide this information.