select
im.port_code AS "港コード",
p.port_name AS "港名",
SUM(CASE WHEN im.kind_code = 110 THEN im.amt ELSE NULL END) AS "出国者数",
SUM(CASE WHEN im.kind_code = 120 THEN im.amt ELSE NULL END) AS "入国者数",
SUM(CASE WHEN im.kind_code = 110 THEN im.amt ELSE NULL END) - SUM(CASE WHEN im.kind_code = 120 THEN im.amt ELSE NULL END) AS "差分"

from
IMMIGRATION AS im
INNER JOIN PORT AS p ON im.port_code = p.port_code
INNER JOIN GRP AS g ON g.group_code = im.group_code
group by im.port_code
Having SUM(CASE WHEN im.kind_code = 110 THEN im.amt ELSE NULL END) - SUM(CASE WHEN im.kind_code = 120 THEN im.amt ELSE NULL END) > 0