ON DUPLICATE KEY UPDATE

1, MySQL special syntax

2. Solved problems

When insert data encounters a unique key constraint (primary key or unique index), perform a change operation for the specified field. If ON DUPLICATE KEY UPDATE is specified at the end of the INSERT statement and DUPLICATE values appear in a UNIQUE index or PRIMARY KEY, perform UPDATE ON the row where DUPLICATE values appear. Insert a new row if it does not cause problems with duplicate columns of unique values.

3, SQL example

INSERT INTO classes (_id,password) 
VALUES 
('1','aaaa') ,
('2','bbbb')
ON DUPLICATE KEY UPDATE 
password =  VALUES(password)
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