使用多个查询还是联合多个查询,哪一个会更快?

多个或 用联合联接的多个查询的查询 会更快吗?我只联接了两个表以使其简单化,但联接中可以有更多的表。

    select isbn, booktitle from book as b left join publisher as p
        on b.publisherid = p.publisherid
        where 
           booktitle like '%mysql%' or
           isbn like '%mysql%' or
           publishername like '%mysql%'  

与

      select isbn, booktitle from book as b left join publisher as p
   on b.publisherid = p.publisherid
   where 
    booktitle like '%mysql%'  
   union 
   select isbn, booktitle from book as b left join publisher as p
   on b.publisherid = p.publisherid
   where 
    isbn like '%mysql%' 
   union 
   select isbn, booktitle from book as b left join publisher as p
   on b.publisherid = p.publisherid
    where 
    publishername like '%mysql%'