前提条件：必须是唯一主键；

CREATE UNIQUE INDEX idx_vote_object ON test_customers_vote (`vote_object`, `vote_object_id`);

用一条sql实现“不存在即插入，存在则increase 某字段”的复合功能 – insert into … on duplicate key update
比如：
CREATE UNIQUE INDEX comp ON logs (`site_id`, `time`);

INSERT INTO logs (`site_id`, `time`,`hits`) VALUES (1,"2004-08-09", 15) ON DUPLICATE KEY UPDATE hits=hits+15;

文章来源：http://hi.baidu.com/caoxin_rain/item/7b7139e99f4763e6fb42ba60