如何使用分隔符將列結果轉換爲單個字符串

Question

我有一個愚蠢的問題，我無法在Teradata中解決。

我有n個表和n個表中的每一個表（n> 1000）我必須得到表的列，這可能因表而異。

我的問題是：我怎樣才能得到結果從一個查詢在一個字符串（像Select columnName from dbc.columns where tablename = table1），讓我們說_vColumns，爲了能夠在以後的價值在排序（_vColumns）在動態使用SQL語法？

Answer 1

我這樣做，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，因爲Td14.10你應該使用dbc.Column V代替（如果你超過30個字符有任何列名更長的時間），然後爲2048 * 128字符將達到64000個字符的最大限制...