SQL SERVER – Generate Different Random Number for Each Group Using RAND() Function

You know that RAND() function in SQL Server generates a random float value 0 through 1 (excluding 0 and 1).

Let us create the following dataset

CREATE TABLE #random(no INT)
INSERT INTO #random(no)
SELECT 1 UNION ALL
SELECT 1 UNION ALL
SELECT 1 UNION ALL
SELECT 2 UNION ALL
SELECT 3 UNION ALL
SELECT 3

If you want to generate a random value, you can use the following code

SELECT no, RAND() AS random_number FROM #random

which results to

no random_number
 1 0.370366365964781
 1 0.370366365964781
 1 0.370366365964781
 2 0.370366365964781
 3 0.370366365964781
 3 0.370366365964781

Please note that when you execute it , you may get different random number than what I got for column 2 but all will be same

What if you want to generate random number in such a way that it is reset to each column value (in this case the column is no)?
Did you know that RAND() accepts a seed value as well?

If you execute the following code,

SELECT no, RAND() AS random_number,RAND(no) AS random_number_reset FROM #random

the result is

no random_number random_number_reset
 1 0.58334760467751 0.713591993212924
 1 0.58334760467751 0.713591993212924
 1 0.58334760467751 0.713591993212924
 2 0.58334760467751 0.713610626184182
 3 0.58334760467751 0.71362925915544
 3 0.58334760467751 0.71362925915544

Please note that when you execute it , you may get different random number than what I got for column2 2 and 3. If you notice the result the values of second column is same for all rows, whereas the values of third column is same withing a group (column no), and different across groups. So if you want to generate random number differently for each group, you can make use of this method.

Reference: Pinal Dave (https://blog.sqlauthority.com)

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