SELECT PORT_CODE AS '港コード', PORT_NAME AS '港名', inamt AS '入国者数', outamt AS '出国者数', inamt - outamt AS '差分'
FROM (SELECT PORT_CODE, AMT AS inamt
      FROM IMMIGRATION
      WHERE KIND_CODE = '110' AND GROUP_CODE = '120')
         JOIN (SELECT PORT_CODE, AMT AS outamt
               FROM IMMIGRATION
               WHERE KIND_CODE = '120' AND GROUP_CODE = '120') AS s
              USING(PORT_CODE)
         JOIN PORT USING(PORT_CODE)
WHERE inamt > outamt
ORDER BY inamt - outamt DESC, PORT_CODE DESC