INSERT INTO .. ON DUPLICATE KEY UPDATE for multiple items

After MySQL 8.0.19, you can use as keyword, for example:

INSERT INTO t1 (a,b,c) VALUES (1,2,3),(4,5,6) AS new
  ON DUPLICATE KEY UPDATE c = new.a+new.b;

or

INSERT INTO t1 (a,b,c) VALUES (1,2,3),(4,5,6) AS new(m,n,p)
  ON DUPLICATE KEY UPDATE c = m+n;

ref: https://dev.mysql.com/doc/refman/8.0/en/insert-on-duplicate.html

Too low on rep for comment, but I wanted to add a slightly more complex syntax that was inspired by @ʞɔıu response. To update multiple fields on duplicate key:

INSERT INTO t (t.a, t.b, t.c, t.d)
VALUES ('key1','key2','value','valueb'), ('key1','key3','value2','value2b')
ON DUPLICATE KEY UPDATE
t.c = VALUES(t.c),
t.d = VALUES(t.d)

Hope that helps someone out there looking to perform bulk insert with multiple on duplicate key update. The syntax escaped me.

Use the VALUES() function

INSERT INTO t (t.a, t.b, t.c)
VALUES ('key1','key2','value'), ('key1','key3','value2')
ON DUPLICATE KEY UPDATE
t.c = VALUES(t.c)

see http://dev.mysql.com/doc/refman/5.0/en/insert-on-duplicate.html