SSIS 2008 or 2012 Data Task: How to conditionally choose one of two flatfile columns on a per-row basis

Question

I searched the textbooks and searchable forum posts for something related to my question, but could not find it. I'm hoping when after I describe my question that it might sound familiar to someone.
First, the context: another department using a black-box database product stopped use of one column and used a different column instead. However, the data in the flat-file export that I need to use for my own database must contain the entire
table. If it was a clean binary switch, that would be great: I could split the rows into two groups based on date and deal with it that way. Instead, there was a period of overlap while users slowly got the hang of the practice.  This means that I have
two columns where a row value is either in one column
or the other.
Now, the question: I currently use SSIS to import this flatfile into an SQL Server table and use a T-SQL script in an SQL Agent Job to handle the problem.
However, I was hoping I could do this on the SSIS side while importing the data so that it appears into the SQL Server destination table nice and clean.
This is a HIGHLY SIMPLIFIED view of my system, using dummy data and dummy names. The T-SQL script describes in essence my source and destination table and what I would like to do on the SSIS side. If a screenshot of my incomplete data tab will help, I can
do it, but at this point I'm providing what I hope presents the background without presenting distractions.  
Thank you for any hints or ideas.
use Learning_Curve;
go
if OBJECT_ID('dbo.Relation_A','U') is not null
drop table dbo.Relation_A;
create table dbo.Relation_A (
Rel_A_ID int primary key,
Rel_A_Value varchar(20) not null,
Rel_B_Value varchar(20) not null
insert into dbo.Relation_A values (1,'Unknown','Measured'),(2,'Measured','N/A'),(3,'Unknown','Measured'),
(4,'Measured','Unknown'),(5,'N/A','Measured'),(6,'Unknown','Measured');
if OBJECT_ID('dbo.Relation_D','U') is not null
drop table dbo.Relation_D;
create table dbo.Relation_D (
Rel_D_ID int primary key,
Rel_D_Value varchar(20) not null
insert into dbo.Relation_D
select
a.Rel_A_ID as Rel_D_ID,
case
when a.Rel_A_Value = 'N/A' or a.Rel_A_Value='Unknown'
then a.Rel_B_Value
else a.Rel_A_Value
end as Rel_D_Value
from dbo.Relation_A a;
go

Answer 1

You could have posted question in new thread.
Anyway, you can achieve it by using below tasks shown in attached picture.
- Merge Join will join by using first ID column
- Derived Column will have below expressions
[Column 1] == "" || ISNULL([Column 1]) ? [AnotherColumn 1] : [Column 1]
[Column 2] == "" || ISNULL([Column 2]) ? [AnotherColumn 1] : [Column 2]
Cheers,
Vaibhav Chaudhari
[MCTS],
[MCP]