Nightmare Case Statement Assistance pl - sql

Question

Table 1 - Deal ID, REF NOS, Type, Papa ID
Table 2 - Deal ID, Type
Making a column in a new view called Method used. The way the field is to be set is as follows ( 4 conditions);
If Deal ID from table 1 Exists in Table 2 and Type is not Null from Table 2.
Set Method used to be Y
If Deal ID does not exist in Table 1 and Type does not contain 27,42 or 55 in Table 1.
Set Method used to be Y
If Papa ID is null from Table 1, and Type does not contain 27,42 or 55 in Table 1.
Set Method used to be Y
Else
Set to N
Started it and thought wow!..
create view Master as (
select Deal ID, REF NOS, Type, Papa ID
[Method used]=
Case
When
from Table 1 A
)

Answer 1

Something like this may work (assuming that these tables join on DealId). Note, I've removed spaces from some of your column names that you showed in your question.
Given these tables:
CREATE TABLE #Table1 (DealId INT, RefNos VARCHAR(100), [Type] VARCHAR(100), PapaId INT);
CREATE TABLE #Table2 (DealId INT, [Type] VARCHAR(100));
view example:
WITH DealIds AS (
SELECT DealId FROM #Table1
UNION
SELECT DealId FROM #Table2
)
SELECT
CASE
-- If Deal ID from table 1 Exists in Table 2 and Type is not Null from Table 2.
-- Set Method used to be Y
WHEN t1.DealId IS NOT NULL AND t2.DealId IS NOT NULL AND t2.[Type] IS NOT NULL THEN 'Y'
-- If Deal ID does not exist in Table 1 and Type does not contain 27,42 or 55 in Table 1.
-- Set Method used to be Y
-- Note: it is is redundant to have the type condition if DealId is the PK.
WHEN t1.DealId IS NULL AND t1.[Type] NOT IN (27, 42, 55) THEN 'Y'
-- If Papa ID is null from Table 1, and Type does not contain 27,42 or 55 in Table 1.
-- Set Method used to be Y
WHEN t1.PapaId IS NULL AND t1.[Type] NOT IN (27,42, 55) THEN 'Y'
-- Else
-- Set to N
ELSE 'N'
END AS MethodUsed
FROM DealIds d
LEFT JOIN #Table1 t1 ON d.DealId = t1.DealId
LEFT JOIN #Table2 t2 ON d.DealId = t2.DealId