CASE expression and no rows selected

Question

Consider the statement:
INSERT INTO target_tab(plan_id)
SELECT
CASE
WHEN customer_type = 'S'
THEN SELECT plan_id FROM tab where customer_id = 12
ELSE 123456
END
FROM
customer_tab
the query
SELECT plan_id FROM tab where customer_id = 12
returs no rows
PROBLEM: if the column target_tab(plan_id) is not nullable
, I cannot insert any data when customer_id is 12.
I would like to insert 0 if the query returs no rows.
I am not able to use NVL on empty set.
How can I solve my problem?

Answer 1

Or how about
SELECT CASE c.customer_type
           WHEN 'S' THEN t.plan_id
           ELSE 123456
       END
FROM   customer_tab c
     , ( SELECT NVL(MIN(plan_id),0) AS plan_id
         FROM   tab
         WHERE  customer_id = 12 ) t;