Use SUM() and UNION ALL in mySQL to get multiple sum columns

Question

I have four tables, all of which contain columns called:
'location'
'sortiment'
'amount_in' (numerical)
'amount_out' (numerical)

All of them represent different instances in wood processing, such as production, storage, loading on railway cars etc, just FYI. Using different SUM(in-out) queries, I can see the amount of different wood sortiments in each location. But I have to add new queries manually everytime a new location is added, such as a new logging area. Basically the tables are all similar to each other, so that I can use UNION ALL to sum up everything everywhere!

Now what I want to do, is creating a table with a single query, that will basically look like this:

|             | location A | location B | location C |
|-------------|------------|------------|------------|
| sortiment A |  sum(AA)   |  sum(AB)   |  sum(AC)   |
| sortiment B |  sum(BA)   |  sum(BB)   |  sum(BC)   |
| sortiment C |  sum(CA)   |  sum(CB)   |  sum(CC)   |

All of the tables contain all sortiments, but every table has different locations.

Here's what I tried first:

SELECT location, sortiment, SUM(amount_in-amount_out)
FROM (
SELECT location, sortiment, amount_in, amount_out FROM Eproduction 
UNION ALL
SELECT location, sortiment, amount_in, amount_out FROM Estorage 
UNION ALL
SELECT location, sortiment, amount_in, amount_out FROM Elogdepot
UNION ALL
SELECT location, sortiment, amount_in, amount_out FROM Erailway
) x
GROUP by location";

and then the loop

echo "<tr><td>".$row['sortiment']. "</td><td>" .(float)$row['SUM(amount_in-amount_out)']."</td></tr>";

obviously resulting in this

| sortiment A | sum(AA) |
| sortiment B | sum(BA) |
| sortiment C | sum(CA) |
| sortiment A | sum(AB) |
| sortiment B | sum(BB) |
| sortiment C | sum(CB) |etc

which is not what I wanted to achieve.

Then I tried aliases:

SELECT location, sortiment, 
SUM(in_pr-out_pr), 
SUM(in_sto-out_sto), 
SUM(in_log-out_log), 
SUM(in_rail-out_rail)
FROM (
SELECT location, sortiment, amount_in AS in_pr, amount_aout AS out_pr FROM Eproduction 
UNION ALL
SELECT location, sortiment, amount_in AS in_sto, amount_out AS out_sto FROM Estorage 
UNION ALL
SELECT location, sortiment, amount_in AS in_log, amount_out AS out_log FROM Elogdepot
UNION ALL
SELECT location, sortiment, amount_in AS in_rail, amount_out AS out_rail FROM Erailway
) x
GROUP by location, sortiment";

and then the loop

echo "<tr><td>".$row['location']. "</td><td>".$row['sortiment']. "</td><td>" .(float)$row['SUM(in_pr-out_pr)']."</td><td>" .(float)$row['SUM(in_sto-out_sto)']."</td><td>" .(float)$row['SUM(in_log-out_log)']."</td><td>" .(float)$row['SUM(in_rail-out_rail)']."</td></tr>";

Which in my understanding should create the table I want, BUT it returns 'unknown field 'in_sto'' error.

Any help appreciated, thanks in advance!