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?
Something like?
select t.*, round(dbms_random.value() * 8) + 1 from foo t;
Edit: David has pointed out this gives uneven distribution for 1 and 9.
As he points out, the following gives a better distribution:
select t.*, floor(dbms_random.value(1, 10)) from foo t;
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(1,10))
Hence:
select output,
count(*)
from (
select floor(dbms_random.value(1,10)) 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
you don’t need a select … from dual, just write:
SELECT t.*, dbms_random.value(1,9) RandomNumber
FROM myTable t
If you just use round then the two end numbers (1 and 9) will occur less frequently, to get an even distribution of integers between 1 and 9 then:
SELECT MOD(Round(DBMS_RANDOM.Value(1, 99)), 9) + 1 FROM DUAL
floor
dbms_random.value()call is only executed once, since theselectit's in is evaluated before the outerselect.