Can you create nested WITH clauses for Common Table Expressions?

Question

WITH y AS (
    WITH x AS (
        SELECT * FROM MyTable
    )
    SELECT * FROM x
)
SELECT * FROM y

Does something like this work? I tried it ear

Answer 1

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