MySQL 8.0

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CREATE TABLE Sales_Line (
  Customer_Number VARCHAR(4),
  Part_Number VARCHAR(4),
  Shipped FLOAT
);

INSERT INTO Sales_Line
  (Customer_Number, Part_Number, Shipped)
VALUES
  ('A080', 'C76', -11.0),
  ('A080', 'C76', -1.0),
  ('A080', 'C76', -2.0),
  ('A080', 'C76', -1.0),
  ('A080', 'C76', -1.0),
  ('A080', 'C76', 21.0),
  ('A080', 'C76', 79.0),
  ('A080', 'C76', 1.0),
  ('A080', 'C76', 11.0),
  ('A080', 'C76', 99.0),
  ('A045', 'X150', -6.0),
  ('A045', 'X150', -1.0),
  ('A045', 'X150', -11.0),
  ('A045', 'X150', -2.0),
  ('A045', 'X150', -1.0),
  ('A045', 'X150', -1.0),
  ('A045', 'X150', -1.0),
  ('A045', 'X150', 373.0),
  ('A045', 'X150', 12.0),
  ('A045', 'X150', 1.0),
  ('A045', 'X150', 300.0),
  ('A045', 'X150', 146.0),
  ('A045', 'X150', 150.0),
  ('A045', 'X150', 150.0),
  ('A045', 'X150', 200.0),
  ('A045', 'X150', 150.0),
  ('A045', 'X150', 150.0);
SELECT Customer_Number, Part_Number,
       SUM(Shipped) Shipped
FROM Sales_Line
GROUP BY Customer_Number, Part_Number, SIGN(Shipped)


Customer_Number
Part_Number
Shipped


A080
C76
-16

A080
C76
211

A045
X150
-23

A045
X150
1632


SELECT Customer_Number, Part_Number,
       SUM(Shipped) Shipped
FROM Sales_Line
GROUP BY Customer_Number, Part_Number, 
         CASE WHEN Shipped < 0 THEN -1 ELSE 1 END


Customer_Number
Part_Number
Shipped


A080
C76
-16

A080
C76
211

A045
X150
-23

A045
X150
1632