如何使用分隔符将类似结果的列获取到单个字符串

Question

我有一个我无法在 Teradata 中解决的愚蠢问题。

我有 n tables，对于 n tables (n>1000) 中的每一个，我必须得到 table 的列，这可能不同于 table 到 table。

我的问题是：如何从字符串中的一个查询（类似于 Select columnName from dbc.columns where tablename = table1）中获取结果，比方说 _vColumns，以便以后能够使用该值在动态 SQL 语法中的排序 (_vColumns) 中？

Answer 1

我 long ago 使用 dbc.columns

 /*** Rows to concatenated string ***/
 /*** Nested version instead of hundreds of CASEs.
       Returns a single concatenated string consisting of up to 2048
 columnnames ***/
SELECT
  databasename
 ,tablename
 ,max(case when rnk mod 16 = 0 then ColumnName else '' end) ||
  max(case when rnk mod 16 = 1 then ',' || ColumnName else '' end) ||
  max(case when rnk mod 16 = 2 then ',' || ColumnName else '' end) ||
  max(case when rnk mod 16 = 3 then ',' || ColumnName else '' end) ||
  max(case when rnk mod 16 = 4 then ',' || ColumnName else '' end) ||
  max(case when rnk mod 16 = 5 then ',' || ColumnName else '' end) ||
  max(case when rnk mod 16 = 6 then ',' || ColumnName else '' end) ||
  max(case when rnk mod 16 = 7 then ',' || ColumnName else '' end)
 as Columns
from
 (
  sel
    databasename
   ,tablename
   ,rnk / 16 as rnk
   ,max(case when rnk mod 16 = 0 then ColumnName else '' end) ||
    max(case when rnk mod 16 = 1 then ',' || ColumnName else '' end) ||
    max(case when rnk mod 16 = 2 then ',' || ColumnName else '' end) ||
    max(case when rnk mod 16 = 3 then ',' || ColumnName else '' end) ||
    max(case when rnk mod 16 = 4 then ',' || ColumnName else '' end) ||
    max(case when rnk mod 16 = 5 then ',' || ColumnName else '' end) ||
    max(case when rnk mod 16 = 6 then ',' || ColumnName else '' end) ||
    max(case when rnk mod 16 = 7 then ',' || ColumnName else '' end) ||
    max(case when rnk mod 16 = 8 then ',' || ColumnName else '' end) ||
    max(case when rnk mod 16 = 9 then ',' || ColumnName else '' end) ||
    max(case when rnk mod 16 = 10 then ',' || ColumnName else '' end) ||
    max(case when rnk mod 16 = 11 then ',' || ColumnName else '' end) ||
    max(case when rnk mod 16 = 12 then ',' || ColumnName else '' end) ||
    max(case when rnk mod 16 = 13 then ',' || ColumnName else '' end) ||
    max(case when rnk mod 16 = 14 then ',' || ColumnName else '' end) ||
    max(case when rnk mod 16 = 15 then ',' || ColumnName else '' end) as ColumnName
  from
   (
    select
      databasename
     ,tablename
     ,rnk / 16 as rnk
     ,max(case when rnk mod 16 = 0 then ColumnName else '' end) ||
      max(case when rnk mod 16 = 1 then ',' || ColumnName else '' end) ||
      max(case when rnk mod 16 = 2 then ',' || ColumnName else '' end) ||
      max(case when rnk mod 16 = 3 then ',' || ColumnName else '' end) ||
      max(case when rnk mod 16 = 4 then ',' || ColumnName else '' end) ||
      max(case when rnk mod 16 = 5 then ',' || ColumnName else '' end) ||
      max(case when rnk mod 16 = 6 then ',' || ColumnName else '' end) ||
      max(case when rnk mod 16 = 7 then ',' || ColumnName else '' end) ||
      max(case when rnk mod 16 = 8 then ',' || ColumnName else '' end) ||
      max(case when rnk mod 16 = 9 then ',' || ColumnName else '' end) ||
      max(case when rnk mod 16 = 10 then ',' || ColumnName else '' end) ||
      max(case when rnk mod 16 = 11 then ',' || ColumnName else '' end) ||
      max(case when rnk mod 16 = 12 then ',' || ColumnName else '' end) ||
      max(case when rnk mod 16 = 13 then ',' || ColumnName else '' end) ||
      max(case when rnk mod 16 = 14 then ',' || ColumnName else '' end) ||
      max(case when rnk mod 16 = 15 then ',' || ColumnName else '' end) as ColumnName
    from
     (
      select
        databasename
       ,tablename
       ,trim(columnName) as ColumnName
       ,rank() over (partition by databasename, tablename
                     order by columnid) -1 as rnk
      from
        dbc.columns 
     ) dt
    group by 1,2,3 
   )dt
  group by 1,2,3
 )dt
group by 1,2

但是，从 Td14.10 开始，您应该改用 dbc.ColumnV（如果您的列名称超过 30 个字符），那么 2048*128 个字符将达到 64000 个字符的最大限制...

如何使用分隔符将类似结果的列获取到单个字符串

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teradata