An expression to be used exclusively in GROUP BY clauses.

The SELECT … GROUP BY clause accepts a variety of expressions, mostly ordinary Field expressions, but also some special expressions usable only in the GROUP BY clause, such as DSL#groupingSets(Field[][]).

Example:

// Assuming import static org.jooq.impl.DSL.*;

using(configuration)
   .select(ACTOR.LAST_NAME)
   .from(ACTOR)
   .groupBy(ACTOR.LAST_NAME) // GroupField reference here
   .fetch();

Instances can be created using DSL#groupingSets(Field[][]) and related methods, or by creating a subtype.