"SELECT id,subjectId,title,content,addTime,author,(SELECT top 1 smallImage FROM pmo_images WHERE pmo_images.topicId = pmo_topic.id) AS smallImage FROM pmo_topic WHERE subjectId = ".$subjectId." ORDER BY addTime DESC LIMIT ".($pageIndex*$pageSize).",".$pageSize
/*
SELECT top 1 smallImage FROM pmo_images WHERE pmo_images.topicId = pmo_topic.id
这个语句的查询结果有可能为空
*/
哈哈,解决了。原来MYSQL 没有 top 1, 要用 limit 1
厉害了,楼主自己解决了^_^