How can I acces the output from the first select statement - sql

Question

I have a table Like this
Col1 | Col2
-----------
a | d
b | e
c | a
Now I want to create an statement to get an output like this:
First| Second
-------------------
a | Amsterdamm
b | Berlin
c | Canada
...
So far I have this consturct what is not working
SELECT *
FROM(
SELECT DISTINCT
CASE
when Col1 IS NULL then 'NA'
else Col1
END
FROM Table1
UNION
SELECT DISTINCT
CASE
when Col2 IS NULL then 'NA'
else Col2
END
FROM Table1
) AS First
,
(
SELECT DISTINCT
when First= 'a' then 'Amsterdam'
when First= 'b' then 'Berlin'
when First= 'c' then 'Canada'
) AS Second
;
can you help me with that
Sorry I have to edit my question to be more specific.

Answer 1

Not as familiar with DB2... I'll lookup if it has a concat function in a sec... and it does.
SELECT First, case when first = 'a' then
concat('This is a ',first)
case when first = 'b' then
concat('To Be or not to ',first)
case else
concat('This is a ',first) end as Second
FROM (
SELECT coalesce(col1, 'NA') as First
FROM Table
UNION
SELECT coalesce(col2, 'NA')
FROM table) SRC
WHERE first <> 'NA'
What this does is generate a single inline view called src with a column called first. If col1 or col2 of table are null then it substitutes NA for that value. It then concatenates first and the desired text excluding records with a first value of 'NA'
Or if you just create an inline table with the desired values and join in...
SELECT First, x.b as Second
FROM (
SELECT coalesce(col1, 'NA') as First
FROM Table
UNION
SELECT coalesce(col2, 'NA')
FROM table) SRC
INNER JOIN (select a,b
from (values ('a', 'This is a'),
('b', 'To B or not to' ),
('c', 'I like cat whose name starts with')) as x(a,b)) X;
on X.a = src.first
WHERE first <> 'NA'
Personally I find the 2nd option easier to read. Though if you have meaning for a,b,c I would think you'd want that stored in a table somewhere for additional access. In code seems like a bad place to store data like this that could change.
Assuming you want
a this is a a
b this is a b
c this is a c
d this is a d
e this is a e

Answer 2

thanks to xQbert
I could solve this problem like this
SELECT FirstRow, concat
(
CASE FirstRow
WHEN 'AN' then 'amerstdam'
WHEN 'G' then 'berlin'
ELSE 'NA'
END, ''
) AS SecondRow
FROM(
Select coalesce (Col1, 'NA') as FirstRow
FROM Table1
UNION
Select coalesce (Col2, 'NA')
FROM Table1) SRC
WHERE FirstRow <> 'NA'
;