INSERT SELECT loop - sql

Question

I am trying to transfer data from one table to another. But in the process I need to do something extra I am just wondering is it possible to do something like this in SQL or PL/SQL alone.
source target
------------------- ------------------------
| id | name | qty | | id | source_id | qty |
------------------- ------------------------
| 1 | test | 2 | | 1 | 1 | 1 |
------------------- ------------------------
| 2 | ago | 1 | | 2 | 1 | 1 |
------------------- ------------------------
| 3 | 2 | 1 |
-----------------------
Here based on the quantity in source table I will have to insert multiple records. Quantity could be of any number. ID in target table is auto incremented. I tried this
INSERT INTO target (SELECT id, qty FROM source);
But this does not take care of the qty loop.

Answer 1

Plain SQL:
with
inputs ( id, qty ) as (
select 1, 2 from dual union all
select 2, 1 from dual union all
select 3, 5 from dual
)
-- end of test data; solution (SQL query) begins below this line
select row_number() over (order by id) as id, id as source_id, 1 as qty
from inputs
connect by level <= qty
and prior id = id
and prior sys_guid() is not null
;
NOTE - if the id is generated automatically, just drop the row_number().... as id column; the rest is unchanged.
ID SOURCE_ID QTY
-- --------- --
1 1 1
2 1 1
3 2 1
4 3 1
5 3 1
6 3 1
7 3 1
8 3 1

Answer 2

This is possible using SQL. Use CTE to generate amount of rows that matches your maximum qty from source table and use non-equi JOIN for generating rows. Use row_number analytic function to assign each row it's unique id (if you have it in your target table, check below on my Edit):
with gen_numbers(r) as (
select rownum r
from dual
connect by rownum <= (select max(qty) from src) -- our maximum limit of rows needed
)
select
row_number() over (order by src.id) as id,
src.id as source_id,
1 as qty
from src
join gen_numbers on src.qty <= gen_numbers.r; -- clone rows qty times
Note that you can safely put in constans value 1 in the output of qty.
Your test data:
create table src (id int, name varchar(255), qty int);
insert into src (id, name, qty)
select 1, 'test', 2 from dual union all
select 2, 'ago', 1 from dual
;
Result:
ID SOURCE_ID QTY
1 2 1
2 2 1
3 1 1
Edit: Since your target id column is auto incremented, you don't need the row_number. Just specify it like that to perform an INSERT:
with gen_numbers(r) as (
select rownum r
from dual
connect by rownum <= (select max(qty) from src) -- our maximum limit of rows needed
)
insert into target_table(source_id, qty)
select
src.id as source_id,
1 as qty
from src
join gen_numbers on src.qty <= gen_numbers.r; -- clone rows qty times
order by src.id
Notice that I've added an ORDER BY clause to ensure proper ordering of inserting values.

Answer 3

INSERT INTO TARGET(source_id, qty)
WITH
output
AS
(
SELECT id, qty FROM source
UNION ALL
SELECT id, qty - 1 FROM source WHERE qty > 1
)
SELECT
id, count(*) as qty
FROM output
group by
id, quantity
ORDER BY
id