@Override
    public <E> Q fullJoin(ForeignKey<E> key, RelationalPath<E> entity) {
        return queryMixin.fullJoin(entity).on(key.on(entity));
    }
Add the given Expression as a query flag

@param position position
@param flag query flag
@return the current object
querydsl-sql/src/main/java/com/querydsl/sql/ProjectableSQLQuery.java