Random allocation of records between two tables - sql

Question

I want to assign the values from Table B to Table A, but so that each record in Table B occurs in the same number of repetitions.
Fiddle SQL

Answer 1

You can use window functions for this and mod arithmetic. For simple repetition:
with a as (
select a.*, rownum as seqnum
from a
),
b as (
select b.*, rownum as seqnum, count(*) over () as cnt
from b
)
select a.col, b.col
from a join
b
on mod(a.seqnum - 1, b.cnt) = b.seqnum - 1;
For more random assignment, randomize the seqnums:
with a as (
select a.*,
row_number() over (order by dbms_random.random) as seqnum
from a
order by db
),
b as (
select b.*, count(*) over () as cnt,
row_number() over (order by dbms_random.random) as seqnum
from b
)
select a.col, b.col
from a join
b
on mod(a.seqnum - 1, b.cnt) = b.seqnum - 1;

Answer 2

You can use the ROWNUM for achieving the same:
SELECT
COLOUR,
EMP
FROM
(
SELECT
COLOUR,
ROWNUM RN
FROM
T1
) T1,
(
SELECT
EMP,
ROWNUM RN
FROM
T2
) T2
WHERE
MOD(T1.RN, 2) + 1 = T2.RN
Fiddler SQL QUERY

Answer 3

Try this,
with Employees as
(select Emp, Row_Number() Over(order by 1) Rn
from B
cross join (select 1
from Dual
connect by level < (select count(1)
from A) / (select count(1)
from B) + 1)
order by Dbms_Random.Value),
Colours as
(select Colour, Rownum Rn
from A)
select t.Colour, k.Emp
from Colours t
join Employees k
on t.Rn = k.Rn