SELeCT 
a.PORT_CODE '港コード' 
,c.PORT_NAME '港名'
,a.AMT '入国者数'
,b.AMT '出国者数'
,a.AMT-b.AMT '差分'
FROM
(
    select 
    PORT_CODE
    ,KIND_CODE
    ,SUM(AMT) AMT
    from IMMIGRATION 
    WHERE GROUP_CODE = 120
    AND KIND_CODE = '110'
    GROUP BY 
    PORT_CODE
    ,KIND_CODE
)a
INNER JOIN
(
    select 
    PORT_CODE
    ,KIND_CODE
    ,SUM(AMT) AMT
    from IMMIGRATION 
    WHERE GROUP_CODE = 120
    AND KIND_CODE = '120'
    GROUP BY 
    PORT_CODE
    ,KIND_CODE
)b
On
a.PORT_CODE = b.PORT_CODE
INNER JOIN
PORT c
ON
a.PORT_CODE = c.PORT_CODE
WHERE
a.AMT-b.AMT>0
ORDER BY  a.AMT-b.AMT desc
,a.PORT_CODE desc