SELECT p.port_code as "港コード",
    p.port_name as "港名",
    table_in.foreign_in as "入国者数",
    table_out.foreign_out as "出国者数",
    table_in.foreign_in-table_out.foreign_out as "差分"
FROM port p
JOIN 
(SELECT port_code, amt as foreign_in FROM immigration i1
JOIN grp g1
ON g1.group_code=i1.group_code
WHERE i1.kind_code = "110" AND g1.group_code="120") table_in
ON table_in.port_code=p.port_code
JOIN
(SELECT port_code, amt as foreign_out FROM immigration i2
JOIN grp g2
ON g2.group_code=i2.group_code
WHERE i2.kind_code = "120" AND g2.group_code="120") table_out
ON table_out.port_code=p.port_code
WHERE table_in.foreign_in > table_out.foreign_out
ORDER BY 差分 DESC, 港コード DESC;