如何在redshift中创建包含列作为值的列？答案

【问题标题】：How create a column containing columns as values in redshift?如何在redshift中创建包含列作为值的列？
【发布时间】：2020-10-13 16:08:11
【问题描述】：

我有如下数据：

id                  start_date   end_date   col1   col2   col3   col4   col5
issue_2017-09       2017-09-18  2017-09-30  true   true   true   true   false

我想将数据转换成以下格式：

id                 start_date    end_date     new_col
issue_2017-09      2017-09-18    2017-09-30   {'col1', 'col2', 'col3', 'col4'}

new_col 是由 [col1, col2, col3, col4, col5] 为真的列创建的。另外我正在使用红移。

【问题讨论】：

标签： amazon-web-services amazon-redshift

【解决方案1】：

我能够使用以下查询解决此问题：

select id, start_date , end_date, listagg(col_name, ', ') as new_col
from (
   select id, start_date, end_date, col1 as val, 'col1' as col_name
   from table
   union all
   select id, start_date, end_date, col2 as val, 'col2' as col_name
   from table
   union all
   select id, start_date, end_date, col3 as val, 'col3' as col_name
   from table
   union all
   select id, start_date, end_date, col4 as val, 'col4' as col_name
   from table
   union all
  select id, start_date, end_date, col5 as val, 'col5' as col_name
   from table
) t
where val is True
group by id, start_date, end_date

【讨论】：

【解决方案2】：

这是另一种方法，

select
  id, start_date, end_date, 
  '{' + 
  case when col1 then '''col1''' else '' end +
  case when col2 then case when col1 then ', ''col2''' else '''col2''' end else '' end +
  case when col3 then case when (col1 or col2) then ', ''col3''' else '''col3''' end else '' end +
  case when col4 then case when (col1 or col2 or col3) then ', ''col4''' else '''col4''' end else '' end +
  case when col5 then case when (col1 or col2 or col3 or col4) then ', ''col5''' else '''col5''' end else '' end +
  '}' as new_col 
 from table01;

【讨论】：