根据变量列多次插入唯一值

Question

我的表中有以下几列：

PromotionID | NumberOfCodes 
1             10
2             5

我需要多次将PromotionID插入新的SQL表中-取决于NumberOfCodes中的值。

因此，鉴于以上所述，我的结果集应显示为：

PromotionID 
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2

Answer 1

您需要递归cte：

with r_cte as (
     select t.PromotionID, 1 as start, NumberOfCodes 
     from table t
     union all
     select id, start + 1, NumberOfCodes 
     from r_cte 
     where start < NumberOfCodes 
)
insert into table (PromotionID)
  select PromotionID
  from r_cte 
  order by PromotionID;

默认递归级别100，如果还有NumberOfCodes，请使用查询提示option(maxrecursion 0)。

Answer 2

我更喜欢这样的事。一旦开始使用较大的行集，rCTe的性能就会很快下降：

WITH N AS(
    SELECT N
    FROM (VALUES(NULL),(NULL),(NULL),(NULL),(NULL),(NULL),(NULL),(NULL),(NULL),(NULL))N(N)),
Tally AS(
    SELECT ROW_NUMBER() OVER (ORDER BY (SELECT NULL)) AS I
    FROM N N1, N N2) --Up to 100 rows. Add more cross joins to N for more rows
SELECT YT.PromotionID
FROM dbo.YourTable YT
     JOIN Tally T ON YT.NumberOfCodes >= T.I;

Answer 3

一个选项使用递归公用表表达式从源表生成行，然后可以将其插入目标表：

with cte as (
    select promotion_id, number_of_codes n from sourcetable 
    union all select promotion_id, n - 1 from mytable where n > 1
)
insert into targettable (promotion_id)
select promotion_id from cte