MySQL -- the use of ON DUPLICATE KEY UPDATE in INSERT

Requirements : Update if it exists, and add it if it does not exist.

Method : It can be easily implemented with kv of redis, and there is such a function in MySQL: ON DUPLICATE KEY UPDATE in INSERT

Conditions of use : where a, b, and c fields must have at least one UNIQUE index or PRIMARY KEY in order to determine record uniqueness

语句：
INSERT INTO table (a,b,c) VALUES (1,2,3) ON DUPLICATE KEY UPDATE c=4

If the row is inserted as a new record, the value of the affected row is 1; if the original record is updated, the value of the affected row is 2

or

You can use the VALUES(col_name) function in the UPDATE clause to reference column values ​​from the INSERT part of the INSERT...UPDATE statement. The VALUES() function is only meaningful in INSERT...UPDATE statements, otherwise it will return NULL

Example:

INSERT INTO table (a,b,c) VALUES (1,2,3),(4,5,6) ON DUPLICATE KEY UPDATE c=VALUES(b) + VALUES(c)