mysql - 使用多个查询或 vs 联合多个查询，哪个会更快？

Question

顾名思义，使用multiple or 的查询会更快，还是使用union joined 的多个查询 会更快？为了简单起见，我只连接了两个表，但连接中可以有更多表。

例如，

    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%'  

对比

      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%'  

Answer 1

我看不出你的工会会更快。您必须扫描并加入 3 次，与第一次一样，您只扫描一次，并且对于每个加入的记录，您都可以应用条件。