Add column from one table to another - powerbi

Question

I have the following tables:
Table A:
___________________
| ID | NUMBER |
|__________|________|
| 10000378 | 1 |
| | |
Table B:
_________________________________________________
| ... | ID | Column 1 | Column 2 |
|____________|__________|____________|____________|
| ... | 10000378 | 7 | 2 |
| | | | |
Table A and Table B share the same ID value.
Not that it matters too much, the ID in Table A is it's key, and can be found in Table B.
Table A's NUMBER column tells me which Table B column to read.
For example:
IF
[Table A].[NUMBER] = 1
THEN
put the value of [Table B].[Column 1] into [Table B].[My Column]
... and so on
As a visual example (my desired result):
_______________________________________________________________
| ... | ID | Column 1 | Column 2 | My Column |
|____________|__________|____________|____________|_____________|
| ... | 10000378 | 7 | 2 | 7 |
| | | | | |
With My Column being the result I am after (which comes from Column 1 - as specified by Table A's NUMBER value for the ID of 10000378).
What I have tried so far
I have set up a 1-to-1 relationship between Table A and Table B (on the ID column`).
I then went into the Power Query Editor tried adding a Conditional Column:
But that doesn't allow me to reference Table A in any way.
So I decided to try the Append Queries as New option:
Selecting the Two tables radio button, setting Primary Table to Table B and Table to append to the primary table to Table B.
With the idea of creating the following structure from which I can get my desired result (but adding the NUMBER column, which I don't really want but can live with):
_____________________________________________________________________________
| ... | ID | Column 1 | Column 2 | NUMBER | My Column |
|____________|__________|____________|____________|_____________|_____________|
| ... | 10000378 | 7 | 2 | 1 | 7 |
| | | | | | |
Doing the append copied all of the contents of Table B and inserted the NUMBER column which is fine, but all the values in that NUMBER column are now null.
I don't understand why this is the case.
How can I achieve my desired result?

Answer 1

Appending queries is used when you have additional rows of data that you’d like to add to an existing query (i.e. union/union all in SQL). Joining tables in Power BI is called "merging":
You can find more details in Combine queries section of Tutorial: Shape and combine data in Power BI Desktop article.
Note that if you have a proper relationship defined between your tables in the model (also described in the article above).

Answer 2

To do this, first merge Table B with Table A and expand the columns you'd like to add to the table (Column 1 and Column 2).
Once you have that, then write your custom column, My Column:
if [NUMBER] = 1 then [Column 1]
else if [NUMBER] = 2 then [Column 2]
else <whatever you want to return if not 1 or 2>