生成随机数列表，使用 SQL 求和到固定数量

Question

这道题是用SQL生成N个和为M(常数)的随机数。

例如我们有一个数字 M=9.754。我们需要 10 个随机数，其总和为 9.754.

应该在SQL服务器环境下完成。

有人能帮帮我吗？

Answer 1

有趣的要求。

下面的查询使用计数table / 数字table 生成10 个随机数，然后找到比率。最终查询检查数字之和不等于@m 的情况，并对最大数字进行调整。

declare @m decimal(10,3) = 9.754,
        @n int           = 10;

with 
-- using recursive CTE to generate a number table
numbers as
(
    select  n   = 1
    union all
    select  n   = n + 1
    from    numbers
    where   n   < @n
),
-- generate random positive numbers using newid()
-- Note : 100 is chosen arbitrary 
num as
(
    select  n = abs(checksum(newid())) % 100
    from    numbers
),
-- calculate the ratio
ratio as
(
    select  r, 
            rn     = row_number() over (order by r desc),
            sum_r  = sum(r) over()
    from
    (
        select  r = convert(decimal(10,3), n * 1.0 / sum(n) over() * @m)
        from    num
    ) r
)
-- sum(r) may not equal to @m due to rounding
-- find the difference and adjust it to the biggest r
select  r, rn, sum_r,
        adj_r     = r + case when rn = 1 then @m - sum_r else 0 end,
        sum_adj_r = sum(r + case when rn = 1 then @m - sum_r else 0 end) over()
from    ratio

dbfiddle demo

Answer 2

虽然@Squirrel 的回答很有趣，但这里的数字更随机这是代码：

DECLARE @s INT=1,
        @k FLOAT=0,
        @final FLOAT=9.917,
        @sum FLOAT =0,
        @min FLOAT=1,
        @max FLOAT=9.917
        
BEGIN
    WHILE (@sum <> @final)
    BEGIN
        WHILE (@s <= 10)
        BEGIN
            
            SET @k =
            (
                SELECT ROUND(RAND(CHECKSUM(NEWID())) * (@max - @min) + @min,3)
            );
            PRINT (CONCAT('random: ',@k));
                    
            IF(@sum+@k <=@final)
                SET @sum+=@k;
            SET @max=@final-@sum;

            PRINT (CONCAT('computed sum: ',@k));
            IF(@max>1) SET @min=1 ELSE SET @min=0;

            IF(@sum=@final)
                BREAK;

            SET @s = @s + 1;
            SET @k = @k + 0;
        END;
        
         PRINT (CONCAT('final', @final))
         PRINT (CONCAT('sum', @sum))

         IF(@sum<>@final)--force stop if after 10 try the sum not match with final
          BEGIN
          PRINT(CONCAT('final random number:',@final-@sum))
          SET @sum=@final;
          END;

         SET @s=0;

         IF(@sum=@final)
            BEGIN
            PRINT('****************************DONE****************************')
            BREAK;
            END
    END;
    PRINT ('end');
END;

生成随机数列表，使用 SQL 求和到固定数量

Generating a list of random numbers, summing to a fixed amount using SQL

sql

sql-server

random