How do I generate random number for each row in a

Question

I need a different random number for each row in my table. The following seemingly obvious code uses the same random value for each row.

SELECT table_name, RAND() magic_number 
FROM information_schema.tables 

I'd like to get an INT or a FLOAT out of this. The rest of the story is I'm going to use this random number to create a random date offset from a known date, e.g. 1-14 days offset from a start date.

This is for Microsoft SQL Server 2000.

Answer 1

try using a seed value in the RAND(seedInt). RAND() will only execute once per statement that is why you see the same number each time.

Answer 2

The Rand() function will generate the same random number, if used in a table SELECT query. Same applies if you use a seed to the Rand function. An alternative way to do it, is using this:

SELECT ABS(CAST(CAST(NEWID() AS VARBINARY) AS INT)) AS [RandomNumber]

Got the information from here, which explains the problem very well.

Answer 3

It's as easy as:

DECLARE @rv FLOAT;
SELECT @rv = rand();

And this will put a random number between 0-99 into a table:

CREATE TABLE R
(
    Number int
)

DECLARE @rv FLOAT;
SELECT @rv = rand();

INSERT INTO dbo.R
(Number)
    values((@rv * 100));

SELECT * FROM R

Answer 4

When called multiple times in a single batch, rand() returns the same number.

I'd suggest using convert(varbinary,newid()) as the seed argument:

SELECT table_name, 1.0 + floor(14 * RAND(convert(varbinary, newid()))) magic_number 
FROM information_schema.tables

newid() is guaranteed to return a different value each time it's called, even within the same batch, so using it as a seed will prompt rand() to give a different value each time.

Edited to get a random whole number from 1 to 14.

Answer 5

Answering the old question, but this answer has not been provided previously, and hopefully this will be useful for someone finding this results through a search engine.

With SQL Server 2008, a new function has been introduced, CRYPT_GEN_RANDOM(8), which uses CryptoAPI to produce a cryptographically strong random number, returned as VARBINARY(8000). Here's the documentation page: https://docs.microsoft.com/en-us/sql/t-sql/functions/crypt-gen-random-transact-sql

So to get a random number, you can simply call the function and cast it to the necessary type:

select CAST(CRYPT_GEN_RANDOM(8) AS bigint)

or to get a float between -1 and +1, you could do something like this:

select CAST(CRYPT_GEN_RANDOM(8) AS bigint) % 1000000000 / 1000000000.0

Answer 6

select round(rand(checksum(newid()))*(10)+20,2)

Here the random number will come in between 20 and 30. round will give two decimal place maximum.

If you want negative numbers you can do it with

select round(rand(checksum(newid()))*(10)-60,2)

Then the min value will be -60 and max will be -50.