Question

我想知道是否可以在此select语句中生成多于一行：

select
      floor(1+(rand()*(1+100-1))) as B1
     ,floor(1+(rand()*(1+100-1))) as B2
     ,floor(1+(rand()*(1+100-1))) as B3
     ,floor(1+(rand()*(1+100-1))) as B4
     ,floor(1+(rand()*(1+100-1))) as B5
     ,floor(1+(rand()*(1+100-1))) as B6 ;

而不是这（单行）

    B1  B2  B3  B4  B5  B6
    -- --   --  --  --  --
    48  35  30  44  31  24

我想看到这个（或者在循环中或者在循环中我想要的很多行）

B1  B2  B3  B4  B5  B6
-- --   --  --  --  --
48  35  30  44  31  24
24  2   34  15  22  15
11  7   2   36  27  26
49  19  44  17  49  47
39  4   48  32  16  34
23  10  32  29  48  9
45  49  13  17  45  25
38  16  15  25  33  41

如果有人知道在没有创建程序的情况下是否可以这样做，我将不胜感激！

Answer 1

大多数数据库提供了一种生成1..n行数据的方法（参见：SQL SELECT to get the first N positive integers），但MySQL并不容易。如果您有一个表，您知道有足够的行来满足您的要求，您可以使用它作为查询的基础，以获得您想要的。

例如，这将为您提供10行：

SELECT @N := @N +1 AS rownumber
     ,floor(1+(rand()*(1+100-1))) as B1
     ,floor(1+(rand()*(1+100-1))) as B2
     ,floor(1+(rand()*(1+100-1))) as B3
     ,floor(1+(rand()*(1+100-1))) as B4
     ,floor(1+(rand()*(1+100-1))) as B5
     ,floor(1+(rand()*(1+100-1))) as B6 
FROM INFORMATION_SCHEMA.COLUMNS, (SELECT @N:=0) dummyRowNums LIMIT 10;

您可以使用任何表来实现此目标，只要您可以确定它的行数超过您希望达到的LIMIT。

如果您在结果集中不需要rownumber，则可以删除SELECT中的第一列并删除连接（＆＃34;，（SELECT @N：= 0）dummyRowNums＆＃34; ）：

SELECT floor(1+(rand()*(1+100-1))) as B1
     ,floor(1+(rand()*(1+100-1))) as B2
     ,floor(1+(rand()*(1+100-1))) as B3
     ,floor(1+(rand()*(1+100-1))) as B4
     ,floor(1+(rand()*(1+100-1))) as B5
     ,floor(1+(rand()*(1+100-1))) as B6 
FROM INFORMATION_SCHEMA.COLUMNS LIMIT 10;

Answer 2

对于SQL Server，使用递归CTE ...并注意RAND函数的种子。

;With integers( num ) as
(
    Select 1 as num
        union all
    Select num + 1
        from integers
        where num <= 10
)
select
      num,
      floor(1+(rand(CHECKSUM(NEWID()))*(1+100-1))) as B1
     ,floor(1+(rand(CHECKSUM(NEWID()))*(1+100-1))) as B2
     ,floor(1+(rand(CHECKSUM(NEWID()))*(1+100-1))) as B3
     ,floor(1+(rand(CHECKSUM(NEWID()))*(1+100-1))) as B4
     ,floor(1+(rand(CHECKSUM(NEWID()))*(1+100-1))) as B5
     ,floor(1+(rand(CHECKSUM(NEWID()))*(1+100-1))) as B6 
    from integers

有关RAND种子问题，请参阅此问题： RAND not different for every row in T-SQL UPDATE

是否可以在没有表的select语句中创建许多行？

2 个答案: