使用 DENSE_RANK() 将数据从行中提取到列中答案

【问题标题】：Using DENSE_RANK() to pull data into columns from rows使用 DENSE_RANK() 将数据从行中提取到列中
【发布时间】：2021-02-04 14:58:08
【问题描述】：

我希望使用 SQL (Oracle) 通过评估特定 ID 上的日期来将数据从行中提取到列中。以下是我的数据目前的样子：

|    ID    |   Date   |   Price   |
-----------------------------------
|   1234   |10/1/2020 |  $12.96   |
|   1234   |10/1/2021 |  $11.32   |
|   1234   |10/1/2022 |  $10.01   |
|   5678   | 6/1/2020 |  $59.96   |

期望的输出：

|    ID    |Yr1 Price |Yr2 Price |Yr3 Price |
---------------------------------------------
|   1234   |  $12.96  |  $11.32  |  $10.01  |
|   5678   |  $59.96  |          |          |

我尝试了几种不同的方法，但都没有成功。我相信 DENSE_RANK() 函数可能是最好的，但会给出一个错误，即它是一个窗口函数并且不允许在那里。所以我遇到了障碍，不确定如何进行。我当前的 SQL 代码是：

 select id, 
       (select price from price_tbl where DENSE_RANK() Over (partition by id) = 1) as yr_1,
       (select price from price_tbl where DENSE_RANK() Over (partition by id) = 2) as yr_2,
       (select price from price_tbl where DENSE_RANK() Over (partition by id) = 3) as yr_3
    from master_tbl

非常感谢任何帮助！

【问题讨论】：

标签： sql oracle oracle11g pivot oracle-sqldeveloper

【解决方案1】：

通过创建包含条件聚合的函数（例如

CREATE OR REPLACE FUNCTION Get_Prices RETURN SYS_REFCURSOR IS
  v_recordset SYS_REFCURSOR;
  v_sql       VARCHAR2(32767);
  v_str       VARCHAR2(32767);
BEGIN
  SELECT LISTAGG( 'MAX(CASE WHEN rn = '||rn||' THEN Price END) AS "Price '||rn||'"' , ',' ) 
          WITHIN GROUP ( ORDER BY 1 )
    INTO v_str
    FROM ( SELECT DISTINCT ROW_NUMBER() OVER (PARTITION BY id ORDER BY 0) AS rn
             FROM master_tbl ); 

  v_sql :=
  'SELECT ID, '|| v_str ||'
     FROM (SELECT p.*,
                  ROW_NUMBER() OVER (PARTITION BY id ORDER BY "Date") AS rn
             FROM master_tbl m )
    GROUP BY id';

  OPEN v_recordset FOR v_sql;
  DBMS_OUTPUT.PUT_LINE(v_sql);
  RETURN v_recordset;
END;
/

然后从 SQL Developer 的命令行调用

VAR rc REFCURSOR
EXEC :rc := Get_Prices;
PRINT rc

【讨论】：

【解决方案2】：

您可以使用row_number() 和条件聚合：

select id, 
       max(case when seqnum = 1 then price end) as yr_1,
       max(case when seqnum = 2 then price end) as yr_2,
       max(case when seqnum = 3 then price end) as yr_3
from (select p.*,
             row_number() over (partition by id order by date) as seqnum
      from price_tbl p
     ) p
group by id;

【讨论】：