SQL Server 2017

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CREATE TABLE reg(
   ATE         INTEGER  NOT NULL 
  ,Article     VARCHAR(6) NOT NULL
  ,Description VARCHAR(5) NOT NULL
  ,Registered  INTEGER  NOT NULL
);
INSERT INTO reg(ATE,Article,Description,Registered) VALUES (1111,'MS1234','SCREW',500);
INSERT INTO reg(ATE,Article,Description,Registered) VALUES (2222,'MS1234','SCREW',600);
INSERT INTO reg(ATE,Article,Description,Registered) VALUES (2222,'AB9999','BOLT',100);
INSERT INTO reg(ATE,Article,Description,Registered) VALUES (3333,'XYZ123','PAINT',900);
INSERT INTO reg(ATE,Article,Description,Registered) VALUES (4444,'LMU232','TOOL',120);
5 rows affected

CREATE TABLE dereg(
   ATE          INTEGER  NOT NULL 
  ,Article      VARCHAR(6) NOT NULL
  ,Description  VARCHAR(5) NOT NULL
  ,Deregistered INTEGER  NOT NULL
);
INSERT INTO dereg(ATE,Article,Description,Deregistered) VALUES (1111,'MS1234','SCREW',260);
INSERT INTO dereg(ATE,Article,Description,Deregistered) VALUES (3333,'XYZ123','PAINT',900);
INSERT INTO dereg(ATE,Article,Description,Deregistered) VALUES (4444,'LMU232','TOOL',20);
INSERT INTO dereg(ATE,Article,Description,Deregistered) VALUES (9999,'TUM933','SHIM',5000);
4 rows affected

select 
    coalesce(r.ate, d.ate) ate, 
    coalesce(r.article, d.article) article, 
    coalesce(r.description, d.description) description, 
    coalesce(r.registered, 0) registered,
    coalesce(d.deregistered, 0) deregistered,
    coalesce(r.registered, 0) - coalesce(d.deregistered, 0) rest
from reg r
full outer join dereg d on d.ate = r.ate and d.article = r.article


ate
article
description
registered
deregistered
rest


1111
MS1234
SCREW
500
260
240

2222
MS1234
SCREW
600
0
600

2222
AB9999
BOLT
100
0
100

3333
XYZ123
PAINT
900
900
0

4444
LMU232
TOOL
120
20
100

9999
TUM933
SHIM
0
5000
-5000

ate	article	description	registered	deregistered	rest
1111	MS1234	SCREW	500	260	240
2222	MS1234	SCREW	600	0	600
2222	AB9999	BOLT	100	0	100
3333	XYZ123	PAINT	900	900	0
4444	LMU232	TOOL	120	20	100
9999	TUM933	SHIM	0	5000	-5000