Generating Random Number In Each Row In Oracle Query

Question

I want to select all rows of a table followed by a random number between 1 to 9:

select t.*, (select dbms_random.value(1,9) num from dual) as RandomNumber
from myTable t

But the random number is the same from row to row, only different from each run of the query. How do I make the number different from row to row in the same execution?

Answer 1

you don’t need a select … from dual, just write:

SELECT t.*, dbms_random.value(1,9) RandomNumber
  FROM myTable t

Answer 2

Something like?

select t.*, round(dbms_random.value() * 8) + 1 from foo t;

Answer 3

At first I thought that this would work:

select DBMS_Random.Value(1,9) output
from   ...

However, this does not generate an even distribution of output values:

select output,
       count(*)
from   (
       select round(dbms_random.value(1,9)) output
       from   dual
       connect by level <= 1000000)
group by output
order by 1

1   62423
2   125302
3   125038
4   125207
5   124892
6   124235
7   124832
8   125514
9   62557

The reasons are pretty obvious I think.

I'd suggest using something like:

floor(dbms_random.value(1,9.9999999999999999))

Hence:

select output,
       count(*)
from   (
       select floor(dbms_random.value(1,9.9999999999999999)) output
       from   dual
       connect by level <= 1000000)
group by output
order by 1

1   111038
2   110912
3   111155
4   111125
5   111084
6   111328
7   110873
8   111532
9   110953