CREATE TABLE  person (
   id int,
   name varchar(20),
   sale int
);
 
CREATE TABLE sale (
   id int,
   `date` date,
   person_id int,
   sale int
 );
 
 INSERT INTO person VALUES (1, 'abc', 0), (2, 'xyz', 0);
 
 INSERT INTO sale VALUES 
 (1, '2016-05-01', 1, 10), 
 (2, '2016-05-02', 1, 10), 
 (3, '2016-05-03', 1, 10), 
 (4, '2016-05-01', 2, 20), 
 (5, '2016-05-02', 2, 20), 
 (6, '2016-05-01', 2, 20);
 
 UPDATE person
 SET sale = (
    SELECT SUM(s.sale) FROM sale s
    WHERE s.person_id = person.id);
 
 
 SELECT * FROM person;
 
 SELECT * FROM sale;
 

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