Oracle SQL - implement logic based on CASE expression result

Question

I have following query which returns me of percentage of rows with at least one NULL in any of columns:

SELECT
(SUM(CASE WHEN tablea.test IS NULL OR tableb.test IS NULL THEN 1 ELSE NULL END)/7000)*100) "at least one NULL (%)"
FROM tablea
FULL OUTER JOIN tableb
ON
tablea.test = tableb.test
WHERE ROWNUM < 7000;

Query works fine to me and I am getting valid result.

But I need to do further action in tablec, based on percentage calculated in my SELECT statement. If percentage of rows with NULL is below 30% I need to insert "YES" string inside table "tablec" column "resultcol", how can I implement such a logic?

Is it for example possible to store SELECT statement result in some temporary variable which will be used in another SQL query?