MYSQL 全文检索， ORDER BY relevance

网上看了教程，自己编写了一段全文检索， ORDER BY relevance的代码，但是搜索结果横竖为0，到底哪里有问题？

我想要：关键字70%符合字段名title,content，30%符合字段名tags。即字段名title,content优先于字段名tags。谢谢。

C# code

SELECT *,
(
(job='worker' AND 
MATCH (title,content) AGAINST ('+$boolean' IN BOOLEAN MODE)* 0.7) 
+ 
(job='worker' AND 
MATCH (tags) AGAINST ('+$boolean' IN BOOLEAN MODE) * 0.3)
) 
AS relevance 
FROM worker_table 
WHERE match (title,content,tags) AGAINST ('+$boolean' IN BOOLEAN MODE) 
AND job='worker' 
ORDER BY relevance DESC

UP+ Waiting help