Can you create nested WITH clauses for Common Table Expressions?

I was trying to measure the time between events with the exception of what one entry that has multiple processes between the start and end. I needed this in the context of other single line processes.

I used a select with an inner join as my select statement within the Nth cte. The second cte I needed to extract the start date on X and end date on Y and used 1 as an id value to left join to put them on a single line.

Works for me, hope this helps.

cte_extract
as 
(
    select ps.Process as ProcessEvent
        , ps.ProcessStartDate 
        , ps.ProcessEndDate 
        -- select strt.*
    from dbo.tbl_some_table ps 
    inner join (select max(ProcessStatusId) ProcessStatusId 
                    from dbo.tbl_some_table 
                where Process = 'some_extract_tbl' 
                and convert(varchar(10), ProcessStartDate, 112) < '29991231'
                ) strt on strt.ProcessStatusId = ps.ProcessStatusID
), 
cte_rls
as 
(
    select 'Sample' as ProcessEvent, 
     x.ProcessStartDate, y.ProcessEndDate  from (
    select 1 as Id, ps.Process as ProcessEvent
        , ps.ProcessStartDate 
        , ps.ProcessEndDate
        -- select strt.*
    from dbo.tbl_some_table ps 
    inner join (select max(ProcessStatusId) ProcessStatusId 
                    from dbo.tbl_some_table 
                where Process = 'XX Prcss' 
                and convert(varchar(10), ProcessStartDate, 112) < '29991231'
                ) strt on strt.ProcessStatusId = ps.ProcessStatusID
    ) x
    left join (
        select 1 as Id, ps.Process as ProcessEvent
            , ps.ProcessStartDate 
            , ps.ProcessEndDate
            -- select strt.*
        from dbo.tbl_some_table ps 
        inner join (select max(ProcessStatusId) ProcessStatusId
                    from dbo.tbl_some_table 
                    where Process = 'YY Prcss Cmpltd' 
                    and convert(varchar(10), ProcessEndDate, 112) < '29991231'
                    ) enddt on enddt.ProcessStatusId = ps.ProcessStatusID
            ) y on y.Id = x.Id 
),

.... other ctes

Nested 'With' is not supported, but you can always use the second With as a subquery, for example:

WITH A AS (
                --WITH B AS ( SELECT COUNT(1) AS _CT FROM C ) SELECT CASE _CT WHEN 1 THEN 1 ELSE 0 END FROM B --doesn't work
                SELECT CASE WHEN count = 1 THEN 1 ELSE 0 END AS CT FROM (SELECT COUNT(1) AS count FROM dual)
                union all
                select 100 AS CT from dual
           )
              select CT FROM A