Oracle 分析函數row_number() over (partition by order by )

一、格式

row_number() over(partition by 列名1 order by 列名2 desc)

二、解析

表示根據 列名1 分組，而後在分組內部根據 列名2 排序，而此函數計算的值就表示每組內部排序後的順序編號,能夠用於去重複值

與rownum的區別在於：使用rownum進行排序的時候是先對結果集加入僞列rownum而後再進行排序，而此函數在包含排序從句後是先排序再計算行號碼．

三、實例

--分析函數
SELECT USER_NAME,
       SCHOOL,
       DEPART,
       ROW_NUMBER() OVER(PARTITION BY USER_NAME ORDER BY SCHOOL, DEPART DESC)
  FROM USER_M;

結果

--分析函數
SELECT *
  FROM (SELECT USER_NAME,
               SCHOOL,
               DEPART,
               ROW_NUMBER() OVER(PARTITION BY USER_NAME ORDER BY SCHOOL, DEPART DESC) RN
          FROM USER_M)
 WHERE RN = 1;

結果

 

--結合分頁
SELECT *
  FROM (SELECT A.USER_NAME,
               A.SCHOOL,
               A.DEPART,
               ROW_NUMBER() OVER(PARTITION BY SCHOOL ORDER BY USER_NAME, DEPART DESC) RN
          FROM (SELECT * FROM USER_M) A
         WHERE ROWNUM <= 10)
 WHERE RN >= 1;

結果