Standard functions allowed in JPQL:
https://docs.jboss.org/hibernate/orm/4.3/devguide/en-US/html/ch11.html#ql-exp-functions

All these functions are supported by Ignite SQL, so can be used in queries.
https://apacheignite-sql.readme.io/docs/numeric-functions
https://apacheignite-sql.readme.io/docs/sql-function

Note that operands may contain other expressions like where upper(substring(h.author.name, length(h.author.name), 1)) = 'A'