[mysql] update/ left join

http://www.mysqltutorial.org/mysql-update-join/

MySQL UPDATE JOIN | Cross-Table Update in MySQL

MySQL UPDATE JOIN syntax

We often use join clauses to query rows in a table that have (in the case of INNER JOIN) or may not have (in the case of LEFT JOIN) corresponding rows in another table. In MySQL, we can use the JOIN clauses in the UPDATE statement to perform the cross-table update.

 

The UPDATE LEFT JOIN  statement basically updates a row in a table when it does not have a corresponding row in another table.

For example, you can increase the salary for a new hire by 1.5%  using the following statement:

UPDATE employees
        LEFT JOIN
    merits ON employees.performance = merits.performance 
SET 
    salary = salary + salary * 0.015
WHERE
    merits.percentage IS NULL;

UPDATE  판매관리  
SET 합계=(SELECT sum(합계) FROM 판매제품관리 WHERE 판매제품관리.판매ID = 판매관리.ID)  
WHERE 날짜='2018-07-01'