mysql插入前判断数据是否存在

业务场景：需要记入访客的访问情况，但不能重复记入

可以插入前进行判断要插入的数据是否存在业务代码如下 ：

INSERT INTO t_topic_vistor(user_id,topic_code) SELECT '218', 
'XQ33019920170811142528217' FROM DUAL WHERE NOT EXISTS(SELECT * 
FROM t_topic_vistor WHERE user_id = 218 and 
topic_code='XQ33019920170811142528217')

语法如下：

INSERT INTO table(field1, field2, fieldn) SELECT 'field1', 
'field2', 'fieldn' FROM DUAL WHERE NOT EXISTS(SELECT field FROM 
table WHERE field = ?)