根据变量列多次插入唯一值

Question

我的表中有以下列：

PromotionID | NumberOfCodes 
1             10
2             5

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

因此，鉴于上述情况，我的结果集应为：

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

Answer 1

你需要递归 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，如果您有更多 NumberOfCodes，请使用查询提示option(maxrecursion 0) 。

Answer 2

我更喜欢对这些事情进行统计。 一旦您开始使用更大的行集，rCTe 的性能就会迅速下降：

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

一种选择使用递归公用表表达式从源表生成行，然后您可以将其插入到目标表中：

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