select * from (
    select
    	t1.PORT_CODE as 港コード
    	,PORT_NAME as 港名
    	,sum(case when KIND_CODE = 110 then AMT else 0 end) as 入国者数
    	,sum(case when KIND_CODE = 120 then AMT else 0 end) as 出国者数
    	,sum(case when KIND_CODE = 110 then AMT else 0 end) - sum(case when KIND_CODE = 120 then AMT else 0 end) as 差分
    from
    	IMMIGRATION as t1
    inner join PORT as t2
    	on t1.PORT_CODE = t2.PORT_CODE
    where 
        t1.GROUP_CODE = 120
    group by
       	t1.PORT_CODE 
    order by
    	差分 desc
    	,港コード desc
)
where 差分 > 0