Oracle SQL use subquery value in another subquery - sql

Question

Before I go any further please mind that I am not well experienced with SQL.
I have one query that is getting a single value (netto value) such as:
WITH cte_value_net AS (
SELECT
nvl(min(value_net),0) as value_net
FROM (
SELECT
i.serial as serial,
nvl(lag(i.value_net) OVER (PARTITION BY i.serial ORDER BY i.month), i.value_net) as value_net
FROM
inventory i
WHERE
i.ctypde IN (
SELECT
ctypde
FROM
appar ap
WHERE
ap.serial = in_serial -- this is the variable I want to set
)
AND
i.month IN (to_char(add_months(sysdate, -1), 'YYYYMM'), to_char(add_months(sysdate, -2), 'YYYYMM'))
AND
i.serial = in_serial -- this is the variable I want to set
) vn
GROUP BY vn.serial
)
In here I have to feed in the variable in_serial that I thought I could get from another subquery such as:
SELECT
(SELECT * FROM cte_value_net) AS value_net
FROM (
SELECT
lap.serial AS in_serial
FROM
applap lap
)
but I can not wrap my head around it why this in_serial is not visible to my custom CTE. Could someone explain me how can I propagate the value from subquery like this?
The error I am obviously getting is:
SQL Error [904] [42000]: ORA-00904: "IN_SERIAL"
Unfortunately I do not have any sample data. What I want to achieve is that I could feed in the returned in_serial from main subquery to my CTE.
Before I can get value_net I need my main query to return the in_serial, otherwise I do not have access to that value.

Answer 1

The trick I use is to produce an extra CTE that I usually call params that includes a single row with all computed parameters. Then, it's a matter of performing a CROSS JOIN with this CTE in any other CTE, subquery or main query, as needed.
For example:
with
params as ( -- 1. Create a CTE that returns a single row
select serial as in_serial from applap
),
cte_value_net AS (
select ...
from inventory i
cross join params -- 2. cross join against the CTE anywhere you need it
where ...
and i.serial = params.in_serial -- 3. Use the parameter
)
select ...

Answer 2

First, your second query is not syntactically correct, as there's a ',' before the FROM. You can write your query like this:
WITH cte_value_net AS (
SELECT
serial, nvl(min(value_net),0) as value_net
FROM (
SELECT
i.serial as serial,
nvl(lag(i.value_net) OVER (PARTITION BY i.serial ORDER BY i.month), i.value_net) as value_net
FROM
inventory i
WHERE
i.ctypde IN (
SELECT
ctypde
FROM
appar ap
WHERE
ap.serial = i.serial
)
AND
i.month IN (to_char(add_months(sysdate, -1), 'YYYYMM'), to_char(add_months(sysdate, -2), 'YYYYMM'))
) vn
GROUP BY vn.serial
)
select ...
from cte_value_net s join applap lap on (lap.serial=s.serial)
(adjust query to your schema ....)