SELECT
 IMM.PORT_CODE as 港コード
 ,PORT_NAME as 港名
 ,ifnull(IMM.AMT,0) as 入国者数
 ,ifnull(IMM2.AMT,0) as 出国者数
 ,ifnull(IMM.AMT,0)-ifnull(IMM2.AMT,0) as 差分
FROM
 IMMIGRATION IMM
JOIN
 IMMIGRATION IMM2
ON
 IMM.PORT_CODE = IMM2.PORT_CODE
 and IMM2.KIND_CODE = '120'
JOIN
 PORT
ON
 IMM.PORT_CODE = PORT.PORT_CODE
WHERE
 IMM.KIND_CODE = '110'
 and ifnull(IMM.AMT,0)>ifnull(IMM2.AMT,0)
ORDER BY
 差分 desc
 ,IMM.PORT_CODE desc;