SELECT
     P.PORT_CODE AS '港コード'
    ,P.PORT_NAME AS '港名'
    ,A.IN_AMT AS '入国者数'
    ,A.OUT_AMT AS '出国者数'
    ,A.DIFF_AMT AS '差分'
FROM
     PORT AS P
     LEFT JOIN (
        SELECT
         I.PORT_CODE 
        ,I.IN_AMT
        ,I.OUT_AMT
        ,(I.IN_AMT - I.OUT_AMT) AS DIFF_AMT
        FROM (
            SELECT
                 I.PORT_CODE 
                ,SUM(CASE WHEN I.KIND_CODE = '110' THEN IFNULL(I.AMT, 0) ELSE 0 END) AS IN_AMT
                ,SUM(CASE WHEN I.KIND_CODE = '120' THEN IFNULL(I.AMT, 0) ELSE 0 END) AS OUT_AMT
            FROM 
                IMMIGRATION AS I
            WHERE 
                I.GROUP_CODE = '120'
            GROUP BY 
                I.PORT_CODE 
        ) AS I
     ) AS A
     ON(P.PORT_CODE = A.PORT_CODE)
WHERE 
     A.DIFF_AMT > 0
ORDER BY 
     A.DIFF_AMT DESC
    ,P.PORT_CODE DESC