根据 teradata 中的日期连接行

Question

我有一个示例表如下：

Date   Type    String  Desired output

01/01   orange  aa      aa
01/10   orange  ab      aa,ab
02/01   orange  bb      aa,ab,bb
02/05   orange  ba      aa,ab,bb,ba
03/15   orange  cc      aa,ab,bb,ba,cc
02/11   apple   aa      aa

所以现在'Date'，'Type'，'String'列是已知的，我想返回所需的输出。我现在可以考虑的可能方法是使用连接函数并尝试了一种方法如下：

select
    t.*,
    row_number()over(partition by Type order by date) as rn,
    lag(string)over(partition by type order by date) as prev_string,
    case when rn = 1 then string when rn = 2 then concat(prev_string, ',', string) end as desired_output
from
    table as t

但是，通过使用上面的代码，它只能在 row_number =2 时返回。如何尝试根据先前的输出附加下一个字符串？我不知道如何解决这部分，并希望获得帮助。如果您能提供其他想法，我将不胜感激！

感谢您的帮助

Answer 1

我知道在 teradata 中执行此操作的唯一方法是使用递归 CTE。

--base data
create volatile table vt_foo 
(dt date,
typ varchar(10),
val varchar(10)
)

on commit preserve rows;

insert into vt_foo values ('2021-01-01','orange','aa');
insert into vt_foo values ('2021-01-10','orange','ab');
insert into vt_foo values ('2021-02-01','orange','bb');
insert into vt_foo values ('2021-02-05','orange','ba');
insert into vt_foo values ('2021-03-15','orange','cc');
insert into vt_foo values ('2021-02-11','apple','aa');

--add row number
create volatile table vt_two as ( select
t.*,
    row_number()over(partition by typ order by dt) as rn
from
    vt_foo as t
) with data
on commit preserve rows;


with  recursive cte (rn , dt ,typ,val, concat_val) as (
select
rn,
dt,
typ,
val,
val as concat_val
from
vt_two
where rn = 1
UNION ALL
select
a.rn,
a.dt,
a.typ,
a.val,
b.concat_val || ',' || a.val
from
vt_two a
inner join cte b
    on a.typ = b.typ
    and a.rn = b.rn + 1
)

select * from cte

order by typ, dt
;