See JdbcTest.testNoCalcBetweenJoins. The plan contains
], customer_id=[$t8], account_num=[$t9], lname=[$t10], fname=[$t11], mi=[$t12], address1=[$t13], address2=[$t14], address3=[$t15], address4=[$t16], city=[$t17], state_province=[$t18], postal_code=[$t19], country=[$t20], customer_region_id=[$t21], phone1=[$t22], phone2=[$t23], birthdate=[$t24], marital_status=[$t25], yearly_income=[$t26], gender=[$t27], total_children=[$t28], num_children_at_home=[$t29], education=[$t30], date_accnt_opened=[$t31], member_card=[$t32], occupation=[$t33], houseowner=[$t34], num_cars_owned=[$t35], fullname=[$t36], product_id=[$t0], time_id=[$t1], customer_id0=[$t2], promotion_id=[$t3], store_id=[$t4], store_sales=[$t5], store_cost=[$t6], unit_sales=[$t7])
EnumerableJoinRel(condition=[=($2, $8)], joinType=[inner])
That calc is just a project. It was probably introduced by a SwapJoinRule. It should be expanded away during code generation, but as it stands the EnumerableCalcRel is expensive.