How can I randomly distribute the figure among rows?

Question

I have a table ABC with column A having following values -
A
a1
a2
a3
a4
a5
a6
I have a fixed figure say for example, 175. I want to randomly generate a value against each of the row so that the sum of values would be 175.
So that I would have output like
A value
a1 12
a2 13
a3 25
a4 100
a5 7
a6 18
or I could have something like
A value
a1 5
a2 30
a3 4
a4 120
a5 11
a6 5
The constrain is that the sum of values should be 175 and the values should be generated randomly.
Can I do this with the single query?

Answer 1

Here a variant that does not give negative results:
SQL> create table abc
  2  as
  3  select 'a1' a from dual union all
  4  select 'a2' from dual union all
  5  select 'a3' from dual union all
  6  select 'a4' from dual union all
  7  select 'a5' from dual union all
  8  select 'a6' from dual
  9  /
Tabel is aangemaakt.
SQL> var N number
SQL> exec :N := 175
PL/SQL-procedure is geslaagd.
SQL> select a
  2       ,   r2
  3         + case max(r) over ()
  4           when r then :N - sum(r2) over ()
  5           else 0
  6           end random_value
  7    from ( select a
  8                , r
  9                , round(r * :N / sum(r) over ()) r2
10             from ( select a
11                         , dbms_random.value r
12                         , rownum  -- to prevent view merging and bugs
13                      from abc
14                  )
15         )
16  /
A                            RANDOM_VALUE
a1                                     35
a2                                     15
a3                                     45
a4                                     36
a5                                      3
a6                                     41
6 rijen zijn geselecteerd.
SQL> /
A                            RANDOM_VALUE
a1                                     16
a2                                     14
a3                                     22
a4                                     40
a5                                     41
a6                                     42
6 rijen zijn geselecteerd.
SQL> /
A                            RANDOM_VALUE
a1                                     25
a2                                     24
a3                                      9
a4                                     28
a5                                     50
a6                                     39
6 rijen zijn geselecteerd.
SQL> /
A                            RANDOM_VALUE
a1                                     44
a2                                      6
a3                                     26
a4                                     39
a5                                     43
a6                                     17
6 rijen zijn geselecteerd.Because I've found that the other one did produce negative values sometimes:
SQL> var N2 number
SQL> exec :N2 := 25
PL/SQL-procedure is geslaagd.
SQL> select a,
  2     case when rn = 1 -- account for rounding errors
  3        then rdm_num1 + (175 - sum(rdm_num1) over ())
  4        else rdm_num1
  5     end rdm_num
  6  from (
  7     select a,
  8        round(rdm /sum(rdm) over (partition by null) * :N) rdm_num1,
  9        rownum rn
10     from (
11        select a,
12           trunc(dbms_random.value(1,:N2)) rdm -- randonm number
13        from abc)
14  )
15  /
A                                 RDM_NUM
a1                                    -64
a2                                     52
a3                                     52
a4                                     20
a5                                     63
a6                                     52
6 rijen zijn geselecteerd.
SQL> /
A                                 RDM_NUM
a1                                     24
a2                                     43
a3                                     34
a4                                     25
a5                                     13
a6                                     36
6 rijen zijn geselecteerd.
SQL> /
A                                 RDM_NUM
a1                                     62
a2                                     41
a3                                      4
a4                                     23
a5                                     26
a6                                     19
6 rijen zijn geselecteerd.
SQL> /
A                                 RDM_NUM
a1                                     -1
a2                                     17
a3                                     49
a4                                     54
a5                                     17
a6                                     39
6 rijen zijn geselecteerd.Regards,
Rob.