主キーがなければINSERTしてあればUPDATE - INSERT ON DUPLICATE KEY UPDATE

 CREATE TABLE t1 ( id1 int UNIQUE, id2 int);

 INSERT INTO t1 ( id1, id2 ) VALUES ( 1, 100 ) ON DUPLICATE KEY UPDATE id2 = id2 + 1;
 
 +------+------+
 | id1  | id2  |
 +------+------+
 |    1 |  100 |
 +------+------+
 
 INSERT INTO t1 ( id1, id2 ) VALUES ( 1, 100 ) ON DUPLICATE KEY UPDATE id2 = id2 + 1;
 
 +------+------+
 | id1  | id2  |
 +------+------+
 |    1 |  101 |
 +------+------+

参考

https://stackoverflow.com/questions/6030071/mysql-table-insert-if-not-exist-otherwise-update