SQL Server 2017

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CREATE TABLE mytable(
   Customer   VARCHAR(47)
  ,Commission NUMERIC(10,2)
  ,Trade_Date DATE 
  , Trade_Type VARCHAR(47)
);

INSERT INTO mytable(Customer,Commission,Trade_Date,Trade_Type) VALUES ('AMIRALIS',20.00,'2018-01-22','SALE');
INSERT INTO mytable(Customer,Commission,Trade_Date,Trade_Type) VALUES ('BRUSSASH',30.00,'2018-01-22','PURCHASE');
INSERT INTO mytable(Customer,Commission,Trade_Date,Trade_Type) VALUES ('AMIRALIS',10.00,'2018-01-22','SALE');
INSERT INTO mytable(Customer,Commission,Trade_Date,Trade_Type) VALUES ('AKBMOBIL',50.00,'2018-01-22','PURCHASE');
INSERT INTO mytable(Customer,Commission,Trade_Date,Trade_Type) VALUES ('AMIRALIS',10.00,'2018-01-23','PURCHASE');
INSERT INTO mytable(Customer,Commission,Trade_Date,Trade_Type) VALUES ('BRUSSASH',10.00,'2018-01-23','PURCHASE');
INSERT INTO mytable(Customer,Commission,Trade_Date,Trade_Type) VALUES ('BRUSSASH',30.00,'2018-01-23','SALE');
INSERT INTO mytable(Customer,Commission,Trade_Date,Trade_Type) VALUES ('BRUSSASH',10.00,'2018-01-23','PURCHASE');
INSERT INTO mytable(Customer,Commission,Trade_Date,Trade_Type) VALUES ('AMIRALIS',60.00,'2018-01-24','PURCHASE');
INSERT INTO mytable(Customer,Commission,Trade_Date,Trade_Type) VALUES ('BRUSSASH',10.00,'2018-01-24','SALE');

10 rows affected

Customer	Total_Commission	Trade_Date	%Commission
AKBMOBIL	50.00	2018-01-22	0.208333
AMIRALIS	30.00	2018-01-22	0.125000
AMIRALIS	10.00	2018-01-23	0.041666
AMIRALIS	60.00	2018-01-24	0.250000
BRUSSASH	30.00	2018-01-22	0.125000
BRUSSASH	50.00	2018-01-23	0.208333
BRUSSASH	10.00	2018-01-24	0.041666