Plain functions can be used in any RAQL query clause. You may use any Presto built-in plain function (see Built-In RAQL Functions for a list) or user-defined plain functions that you or other Presto developers have added.

Simple examples of using plain functions in Select clauses are shown in Use Plain Functions to Update, Select or Sort Rows. Plain functions can also be nested, such as this example which uses both the monthname and the substr plain functions to derive a three-character English name for the birth month of each legislator: