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

1、格式

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

2、解析

表示根据 列名1 分组，然后在分组内部根据 列名2 排序，而此函数计算的值就表示每组内部排序后的顺序编号,可以用于去重复值

与rownum的区别在于：使用rownum进行排序的时候是先对结果集加入伪列rownum然后再进行排序，而此函数在包含排序从句后是先排序再计算行号码．

3、实例

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

结果

--分析函数
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;

结果

--结合分页
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;

结果