Creating Random Set Values For Each Cross Join from CTE

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The question:

I am trying to load up a table with values that are generated randomly based on another table. The issue is that the result set from the final Cross Join, is not unique (random) for each of the rows of the final cross joined table.

Deconstructed CTE
; with MinMax as   -- Step one get the range of values for each `DetailCategoryId`
(
     select distinct DetailCategoryId,
      min(DetailId) over(partition by DetailCategoryId) as [Min] 
    , max(DetailId) over(partition by DetailCategoryId) as [Max]
    from Ref.Detail
)

, RandProcess as   -- Step two pick a random number between the range for each
(
    select MM.DetailCategoryId
      ,   (MM.[Min] + FLOOR(RAND() * (MM.[Max] + 1 - MM.[Min]))) as Rando
    from MinMax MM
)

The final step is to create a cross reference table by Cross JOIN that will give the set of RandProcess into each item. .

select  PRJ.ProjectId, RD.DetailCategoryId, RD.Rando
from info.Project PRJ
CROSS JOIN RandProcess RD

The issue is that each set of data in the PRJ table is the same. Here is the first two rows of each set PRJ data.

10000   101 7
10000   102 10
...
10001   101 7
10001   102 10
...
10002   101 7
10002   102 10
Question

How can I get each of the PRJs sets to be different (random) for each of the PRJ’s rows?

10000   101 7
10000   102 10
...
10001   101 4
10001   102 11
...
10002   101 1
10002   102 14
Why

My goal is to insert these values into another table as test values for each of the PRJ data elements.

The Solutions:

Below are the methods you can try. The first solution is probably the best. Try others if the first one doesn’t work. Senior developers aren’t just copying/pasting – they read the methods carefully & apply them wisely to each case.

Method 1

RAND() is evaluated once and hence you get the same value for all rows.

You can use newid() to simulate a random value. checksum() to convert it to integer and abs() to return absolute value. To get into the your required minimum and maximum range

(ABS(CHECKSUM(NEWID())) % (MM.[Max] - MM.[Min] + 1)) + MM.[Min]

Changes to your RandProcess cte

RandProcess as   -- Step two pick a random number between the range for each
(
    select MM.DetailCategoryId
      ,   (ABS(CHECKSUM(NEWID())) % (MM.[Max] - MM.[Min] + 1)) + MM.[Min] as Rando
    from MinMax MM
)


All methods was sourced from stackoverflow.com or stackexchange.com, is licensed under cc by-sa 2.5, cc by-sa 3.0 and cc by-sa 4.0

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