

Forum Newbie
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Last Login: Tuesday, June 30, 2015 7:52 AM
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Hello, I have a table with 1 million records. For each of these records I want to generate a random number. This random number can be between 0 and 9 Each of these numbers, however, should get a chance to drop. For example, the 0 to have a 15% chance. The 1 is a 20% chance ... How I would do it in TSQL? I think of a scalar function. My approach:
DECLARE @RandomNumber float DECLARE @RandomInteger int DECLARE @MaxValue int DECLARE @MinValue int SET @MaxValue = 9 SET @MinValue = 0 SELECT @RandomNumber = RAND() SELECT @RandomInteger = ((@MaxValue + 1)  @MinValue) * @RandomNumber + @MinValue SELECT @RandomInteger Now has the chance to be accommodated ... But how .. ? :(




Mr or Mrs. 500
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I'm sure there's a more elegant way to do this but here's one possibility. It involves randomly selecting a number between 0 and 9 using 100 of those 10 numbers distributed according to your chance criteria. For this example, I used the chance percent values as follows:
No.  % 0  15 1  20 2  5 3  5 4  25 5  5 6  10 7  5 8  5 9  5
Then in the code, I used the chance percentages to determine how many of those numbers to include in the Substring that selects the random number. The query below will give you the distribution of each of those numbers out of a million records. If you calculate the percentages for each out of the total, you'll see they very closely match the percentages above.
Build cteTally with 1M rows With E1(N) As ( Select 1 Union All Select 1 Union All Select 1 Union All Select 1 Union All Select 1 Union All Select 1 Union All Select 1 Union All Select 1 Union All Select 1 Union All Select 1 ), E2(N) As ( Select 1 From E1 a, E1 b ), E4(N) As ( Select 1 From E2 a, E2 b ), E6(N) As ( Select 1 From E4 a, E2 b ), cteTally(N) As ( Select Row_Number() Over (Order By (Select Null)) From E6 ), Do the select for the numbers from 09 based on the requested distribution chance As ( Select Substring('0000000000000001111111111111111111122222333334444444444444444444444444555556666666666777778888899999', Cast(Floor((Rand(Checksum(Newid()))*100) + 1) as tinyint),1) as test_group From cteTally )
Check the results Select test_group, Count(test_group) as total From chance Group by test_group Order by test_group ;




Ten Centuries
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Hi
I've tried a slightly different approach. This will allow set of values with a chance value (weight) against to be used.
;WITH chances(RES, CHANCE) AS (  Range of values to generate and chance of being picked.  This is not a percentage but odds. eg 'You' has a 20 in 81 chance SELECT RES, CHANCE FROM ( VALUES ('Me', 2 ), ('You', 20), ('Them', 18), ('Others', 1 ), ('Everyone', 30), ('Nobody', 10) ) AS a(RES, CHANCE) ),  Create a table of ranges for the results chancerange(RES,rLow,rHigh) AS ( SELECT a.RES, CAST(SUM(ISNULL(b.chance,0)) AS FLOAT) rLow, CAST(SUM(ISNULL(b.chance,0)) + a.Chance AS FLOAT) rHigh FROM chances a LEFT OUTER JOIN Chances b ON b.RES < a.RES GROUP BY a.RES, a.Chance ),  Generate a random number for each record in the target table randomNum AS ( SELECT RAND(Checksum(Newid())) * c.T SeedResult, a.* FROM Tally a  REPLACE WITH TABLE TO GENERATE NUMBERS FOR CROSS APPLY (SELECT SUM(CHANCE) T FROM Chances) c ),  Build the results randomResults AS ( SELECT (SELECT RES FROM chancerange WHERE SeedResult BETWEEN rLow AND rHigh) RandomResult, * FROM randomNum ) SELECT RandomResult, count(*) num, cast(count(*) / 10000.00 as decimal(4,2)) pct FROM randomResults GROUP BY RandomResult
I've used a Tally table in here to test it, but this can be replaced with any other table.



