SELECT
IM.PORT_CODE `港コード`,
P.PORT_NAME `港名`,
SUM(CASE WHEN IM.KIND_CODE = '110' THEN IM.AMT ELSE 0 END) `入国者数`,
SUM(CASE WHEN IM.KIND_CODE = '120' THEN IM.AMT ELSE 0 END) `出国者数`,
SUM(CASE WHEN IM.KIND_CODE = '110' THEN IM.AMT ELSE 0 END) - SUM(CASE WHEN IM.KIND_CODE = '120' THEN IM.AMT ELSE 0 END) `差分`

FROM
IMMIGRATION IM

JOIN
PORT P
ON IM.PORT_CODE = P.PORT_CODE

WHERE
IM.GROUP_CODE = '120'

GROUP BY
IM.PORT_CODE

HAVING
SUM(CASE WHEN IM.KIND_CODE = '110' THEN IM.AMT ELSE 0 END)
-
SUM(CASE WHEN IM.KIND_CODE = '120' THEN IM.AMT ELSE 0 END)
>
0

ORDER BY
`差分` DESC,
`港コード` DESC