MySQL 如何修改SQL语句，去掉语句中的or

Question

问题遇到的现象和发生背景

MySQL 如何修改SQL语句，去掉语句中的or，因为有or导致索引失效

问题相关代码，请勿粘贴截图

select bid from book a ,querybook b where ( a.bname in (b.bname) or b.bname = "" ) and
(a.bauthor in (b.bauthor) or b.bauthor = "" ) and
(a.barea in (b.barea) or b.barea = "" )
SQL作用是当查询条件为空时默认查询全部数据，不为空是则按照条件进行查询

Answer 1

不知道你想表达什么意思，为什么要判断为空
但是你可以这样

select bid from book a ,querybook b 
where  a.bname in (b.bname) and a.bauthor in (b.bauthor) and a.barea in (b.barea) 
UNION
select bid from book a ,querybook b 
where  b.barea = "" and b.bname = "" and b.bauthor = ""

代码仅供参考，你可以举一反三