How to join multiple sub queries as a single one without 'with'? - sql

Question

I have a query consisting of multiple subqueries. I used 'join' as im not allowed to use 'with'. The subqueries have 'from' clause which is creating an issue.
I have to display two columns with each column consisting certain logic to be displayed. For printing the two columns, i need to use sub queries which requires 'from' clause. I'm not sure how to write the 'from' clause to fit the whole query and make it runnable. I have checked the individual queries and they all work fine.
select lead(dt) over
(partition by t1.id_user order by f.topup_date desc rows between 0
preceding and unbounded following )
from
(select *,
(max(case when f.topup_value >= 20 then f.topup_date end) over (partition
by f.id_user order by f.topup_date desc rows between 0 preceding and
unbounded following )) as dt
from topups f) as f, //(<-I think this is incorrect)
CAST(f.topup_value as float)/CAST(t1.topup_value as float) from
(SELECT t1.seq,t1.id_user,t1.topup_value,row_number()
over (partition by t1.id_user order by t1.topup_date )
as rowrank from topups t1) as t1
inner join topups f on f.id_user=t1.id_user
inner join topups t2 on t1.seq=t2.seq

Answer 1

You're getting a syntax error because a query can only have a single FROM clause. It's difficult to tell the outcome you're trying to achieve, but turning the first query into a non-correlated subquery and using it for column f might be what you're looking for:
select
(select lead(dt) over (partition by t1.id_user order by f.topup_date desc rows between 0 preceding and unbounded following )
from (
select *,
(max(case when f.topup_value >= 20 then f.topup_date end) over (partition by f.id_user order by f.topup_date desc rows between 0 preceding and unbounded following )) as dt
from topups f
) x) as f,
CAST(f.topup_value as float)/CAST(t1.topup_value as float)
from (
SELECT t1.seq, t1.id_user, t1.topup_value, row_number() over (partition by t1.id_user order by t1.topup_date ) as rowrank
from topups t1
) as t1
inner join topups f on f.id_user=t1.id_user
inner join topups t2 on t1.seq=t2.seq

Answer 2

Really hard to read that query. What you marked as possible incorrectness is wrong because you're trying to add what looks like another SELECT after your original FROM clause. That's incorrect syntax. Think of your FROM subquery as a temporary table. You couldn't say something like:
SELECT some_column
FROM a_table, some_other_column
That's cross-join syntax. some_other_column would need to be a table for that to even be valid.
Consider adding a CREATE TABLE and sample data so we can test.
You might be looking for something along the lines of this:
SELECT LEAD(temp.dt) OVER(PARTITION BY temp.id_user ORDER BY temp.topup_date DESC ROWS BETWEEN 0 PRECEDING AND UNBOUNDED FOLLOWING)
, temp.division
FROM
(
SELECT (max(CASE WHEN f.topup_value >= 20 THEN f.topup_date END) OVER(PARTITION BY f.id_user ORDER BY f.topup_date DESC ROWS BETWEEN 0 PRECEDING AND UNBOUNDED FOLLOWING )) AS dt
, f.topup_value::float / t1.topup_value::float AS division
, t1.id_user
, f.topup_date
FROM topups t1
JOIN topups f USING (id_user)
) temp
;
Just an opinion but its less noisy to use the :: operator to cast variables. Instead of CAST(f.topup_value as float) just use f.topup_value::float