How to join table with result column in oracle - sql

Question

I used case when to get a column named 'code' in oracle. Now I want to get another column from a table which need to be joined with the result 'code' column.
Example:
select
(case when field='A' then '001'
when field='B' then '002'
end) code
from table_code
Now I want to get another column 'code_name' in this query from table 'names' containing data as
code: 001= code_name: aa & code: 002= code_name: bb

Answer 1

WITH clause is here just to generate some sample data, and as such, it is not a part of the answer.
Just guessing what you are asking for, but if I got it right the answer is below.
First the sample data:
WITH
ids_data AS
(
Select 'A' "CODE_ID", 'ABCD_123' "SOME_FLD", 10 "AMOUNT" From Dual Union All
Select 'B' "CODE_ID", 'BCD_123' "SOME_FLD", 25 "AMOUNT" From Dual Union All
Select 'C' "CODE_ID", 'CD_123' "SOME_FLD", 10 "AMOUNT" From Dual Union All
Select 'D' "CODE_ID", 'D_123' "SOME_FLD", 30 "AMOUNT" From Dual Union All
Select 'E' "CODE_ID", 'X123' "SOME_FLD", 15 "AMOUNT" From Dual U
),
names_data AS
(
Select '001' "CODE_ID", 'Code Name 001' "CODE_NAME" From Dual Union All
Select '002' "CODE_ID", 'Code Name 002' "CODE_NAME" From Dual Union All
Select '003' "CODE_ID", 'Code Name 003' "CODE_NAME" From Dual Union All
Select '004' "CODE_ID", 'Code Name 004' "CODE_NAME" From Dual Union All
Select '005' "CODE_ID", 'Code Name 005' "CODE_NAME" From Dual U
)
The answer is - just use the CASE statement in the join condition ON clause like you did it in the select clause.
SELECT
i.CODE_ID "CODE_ID",
CASE
WHEN i.CODE_ID = 'A' THEN '001'
WHEN i.CODE_ID = 'B' THEN '002'
WHEN i.CODE_ID = 'C' THEN '003'
WHEN i.CODE_ID = 'D' THEN '004'
WHEN i.CODE_ID = 'E' THEN '005'
ELSE
'000'
END "CODE_ID_2",
n.CODE_NAME "CODE_NAME",
i.SOME_FLD "SOME_FFLD",
i.AMOUNT "AMOUNT"
FROM
ids_data i
INNER JOIN
names_data n
ON(n.CODE_ID = CASE
WHEN i.CODE_ID = 'A' THEN '001'
WHEN i.CODE_ID = 'B' THEN '002'
WHEN i.CODE_ID = 'C' THEN '003'
WHEN i.CODE_ID = 'D' THEN '004'
WHEN i.CODE_ID = 'E' THEN '005'
ELSE
'000'
END)
Here is the result
--
-- R e s u l t :
--
-- CODE_ID CODE_ID_2 CODE_NAME SOME_FFLD AMOUNT
-- ------- --------- ------------- --------- ----------
-- A 001 Code Name 001 ABCD_123 10
-- B 002 Code Name 002 BCD_123 25
-- C 003 Code Name 003 CD_123 10
-- D 004 Code Name 004 D_123 30
-- E 005 Code Name 005 X123 15