Oracle sql case over a computed column - sql

Question

I Want to write in oracle sql, case over a computed column. The query is as follow.
Select trunc (Cost*100/Amt) as 'Computed_LTV',
Case
When Request_Term <19 THEN '60'
When Request_Term <=24THEN'-18'
When Computed_LTV <70.805 THEN '-20'
ELSE '-60'
END AS "Var_1"
FROM LOAN_APP

Answer 1

It is used only once, so I'd suggest you use the same formula:
SELECT TRUNC (Cost * 100 / Amt) AS Computed_LTV,
CASE
WHEN Request_Term < 19 THEN '60'
WHEN Request_Term <= 24 THEN '-18'
WHEN TRUNC (Cost * 100 / Amt) < 70.805 THEN '-20' --> here
ELSE '-60'
END AS Var_1
FROM LOAN_APP
If you insist on using a computed column, you'll have to use a CTE or an inline view, but that's probably a little bit too much in this simple case.
Also, get rid of double quotes in Oracle. They cause nothing but problems.
In order to sum several computed columns, do exactly that: sum them up. For example:
select trunc(cost * 100 / amt) as var1,
round(amount * price) as var2,
--
-- sum them using the "+" operator
(trunc(cost * 100 / amt) + round(amount * price)) as result
from ...
Or, if you computed them in a CTE, you'd then
with data as
(select trunc(cost * 100 / amt) as var1,
round(amount * price) as var2
from ...
)
-- now sum them up
select var1 + var2 as result
from data

Answer 2

You cannot re-use a column alias in the SELECT. But starting in Oracle 12C, you can use a lateral join to define it in the FROM clause:
SELECT x.Computed_LTV,
(Case When Request_Term < 19 THEN '60'
When Request_Term <= 24 THEN'-18'
When Computed_LTV < 70.805 THEN '-20'
ELSE '-60'
END) AS Var_1
FROM LOAN_APP la CROSS JOIN LATERAL
(SELECT TRUNC(Cost*100/Amt) as Computed_LTV FROM DUAL) x;
Note: Do not escape identifiers -- using either single quotes or double quotes. That just clutters queries, making them harder to write and to read.