public C distinctOn(Expression<?>... exprs) {
        return addFlag(Position.AFTER_SELECT,
            Expressions.template(Object.class, "distinct on({0}) ",
            ExpressionUtils.list(Object.class, exprs)));
    }
adds a DISTINCT ON clause

@param exprs
@return
querydsl-sql/src/main/java/com/querydsl/sql/postgresql/AbstractPostgreSQLQuery.java