SELECT
	  a2.港コード
	, a2.港名
	, a2.入国者数
	, a2.出国者数
	, a2.入国者数 - a2.出国者数 '差分' 
FROM
	( 
		SELECT
			  a.PORT_CODE '港コード'
			, a.PORT_NAME '港名'
			, sum( 
				CASE 
					WHEN b.KIND_CODE = '110' 
						THEN b.AMT 
					ELSE 0 
					END
			) '入国者数'
			, sum( 
				CASE 
					WHEN b.KIND_CODE = '120' 
						THEN b.AMT 
					ELSE 0 
					END
			) '出国者数' 
		FROM
			PORT a 
			LEFT JOIN IMMIGRATION b 
				ON a.PORT_CODE = b.PORT_CODE 
			LEFT JOIN GRP c 
				ON b.GROUP_CODE = c.GROUP_CODE 
				AND c.GROUP_CODE = '120' 
		GROUP BY
			a.PORT_CODE
			, a.PORT_NAME
	) a2 
ORDER BY
	5 DESC
	, 1 DESC;