Sql 如何为特定数字范围生成十进制数字序列

考虑上面问题的以下示例。 假设我们有一系列十进制数，比如12.50、13.20等等。 我想要结果

12.51001
12.51002
....
13.19999
13.20000

最多可生成小数点后5位。 在sql中可能吗？

这里有一个使用递归CTE的技巧

在CTE中将数据转换为小数点后5位，以获得所需格式的结果

;WITH cte
     AS (SELECT Cast(12.50 AS NUMERIC(22, 5)) AS num --Min value from your data
         UNION ALL
         SELECT Cast(num + 0.00001 AS NUMERIC(22, 5))
         FROM   cte
         WHERE  num < Cast(13.20 AS NUMERIC(22, 5))) -- Max value from your data
SELECT *
FROM   cte
OPTION (maxrecursion 0) 

---

使用数字表或递归cte

; with rcte as
(
    select  n = 1250000
    union all
    select  n = n + 1
    from    rcte
    where   n   < 1320000
)
select  convert(decimal(10,5), n / 100000.0)
from    rcte
option (maxrecursion 0)

---

我建议不要使用循环来生成序列，而是使用计数表。Aaron Bertrand已经测试了生成集合的各种方法，它的性能远远超过了递归CTE。事实上，递归CTE非常糟糕，它会从大多数结果中删除，因为它会使图上的比例扭曲太多

因此，您可以使用以下方法：

DECLARE @StartNumber DECIMAL(10, 5) = 12.50,
        @EndNumber DECIMAL(10, 5) = 13.20,
        @Increment DECIMAL(10, 5) = 0.00001;

WITH N1 AS (SELECT N FROM (VALUES(1),(1),(1),(1),(1),(1),(1),(1),(1),(1)) n (N)),
N2 (N) AS (SELECT 1 FROM N1 AS N1 CROSS JOIN N1 AS N2),
N3 (N) AS (SELECT 1 FROM N2 AS N1 CROSS JOIN N2 AS N2),
N4 (N) AS (SELECT 1 FROM N3 AS N1 CROSS JOIN N3 AS N2)

SELECT TOP (1 + CONVERT(INT, CEILING((@EndNumber - @StartNumber) / @Increment)))
        @StartNumber + ((ROW_NUMBER() OVER(ORDER BY N) - 1) * @Increment)
FROM    N4;

---

作为您需求的快速基准，如果我将结束编号更改为23.2，则在我的机器上运行这始终需要大约4秒，递归CTE大约需要10秒来生成相同的集合。

我建议使用Tall而不是递归。看，我看了，这很有趣，但我在CTE上注意到，他在SQL中输入了一个“ORDER BY n”-他真的不需要，这花了所有的时间-只需要对最终结果进行排序。理货表最终会缓存在RAM中，因此会使用资源——这就是我反对日历和数字表的原因。

DECLARE @startnum decimal(18,5)=12.50
DECLARE @endnum decimal(18,5)=13.20

set @startnum = @startnum+0.01

 ;WITH cte
 AS (SELECT Cast(@startnum AS NUMERIC(22, 5)) AS num
     UNION ALL
     SELECT Cast(num + 0.00001 AS NUMERIC(22, 5))
     FROM   cte
     WHERE  num < Cast(@endnum AS NUMERIC(22, 5)))
 SELECT *
 FROM   cte
 OPTION (maxrecursion 0) 

DECLARE @StartNumber DECIMAL(10, 5) = 12.50,
        @EndNumber DECIMAL(10, 5) = 13.20,
        @Increment DECIMAL(10, 5) = 0.00001;

WITH N1 AS (SELECT N FROM (VALUES(1),(1),(1),(1),(1),(1),(1),(1),(1),(1)) n (N)),
N2 (N) AS (SELECT 1 FROM N1 AS N1 CROSS JOIN N1 AS N2),
N3 (N) AS (SELECT 1 FROM N2 AS N1 CROSS JOIN N2 AS N2),
N4 (N) AS (SELECT 1 FROM N3 AS N1 CROSS JOIN N3 AS N2)

SELECT TOP (1 + CONVERT(INT, CEILING((@EndNumber - @StartNumber) / @Increment)))
        @StartNumber + ((ROW_NUMBER() OVER(ORDER BY N) - 1) * @Increment)
FROM    N4;