Connect by lead incremental values Oracle - sql

Question

I have this table
COL1 COL2
---------
A 1
B 5
C 12
D 14
And I would like to obtain this other one. This is, until the next col2 for each col1 is reached, a row with the COL1 and incremental values.
COL1 COL2
---------
A 1
A 2
A 3
A 4
B 5
B 6
B 7
B 8
B 9
B 10
B 11
C 12
C 13
D 14
EDIT: this is what I've tried so far. It seems I'm not far away from the solution but struggling to progress further than this.
WITH aux (
col1,
col2
) AS (
SELECT
'A',
1
FROM
dual
UNION ALL
SELECT
'B',
5
FROM
dual
UNION ALL
SELECT
'C',
12
FROM
dual
UNION ALL
SELECT
'D',
14
FROM
dual
), aux1 AS (
SELECT
a.*,
nvl(LEAD(a.col2) OVER(
ORDER BY
a.col2
), a.col2) h
FROM
aux a
)
SELECT
*
FROM
aux1
CONNECT BY level >= col2
AND level <= h;

Answer 1

testseq is the table containing your initial 4 rows. Use lead to find the stop value for col2 for each col1, and recursion to iterate and create the additional rows.
WITH xrows (col1, col2, lastcol2) AS (
SELECT t.*, LEAD(col2) OVER (ORDER BY col1) - 1
FROM testseq t
UNION ALL
SELECT col1, col2+1, lastcol2
FROM xrows t
WHERE col2 < lastcol2
)
SELECT col1, col2
FROM xrows
ORDER BY col1, col2
;

Answer 2

First you need to find the "next" number (whatever ordering you prefer) and then generate such number of rows with recursive subquery:
with a(code, num) as(
select 'A', 1 from dual union all
select 'B', 5 from dual union all
select 'C', 12 from dual union all
select 'D', 14 from dual
)
, b as (
select
a.*
, lead(num - 1, 1, num) over(order by code asc) as next_num
from a
)
select
b.code
, gen.val
from b
cross join lateral(
select num + level - 1 as val
from dual
connect by num + level - 1 <= next_num
) gen
order by 2 asc
Or if you prefer recursive CTE:
with a(code, num) as(
select 'A', 1 from dual union all
select 'B', 5 from dual union all
select 'C', 12 from dual union all
select 'D', 14 from dual
)
, b(code, next_num, val) as (
select
a.code
, lead(num - 1, 1, num) over(order by code asc) as next_num
, num
from a
union all
select
code
, next_num
, val + 1
from b
where val < next_num
)
select
b.code
, val
from b
order by 2 asc
CODE
VAL
A
1
A
2
A
3
A
4
B
5
B
6
B
7
B
8
B
9
B
10
B
11
C
12
C
13
D
14
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