如何优化具有日期内部选择查询的查询？

Question

查询是：

select sum(value) 
  from TAB 
 where TimeStamp=
     {
         select max(TimeStamp)
           from TAB where col1=12 and col2=18
     }
   and col1=12 and col2=18;

我试图通过消除子查询来改进它。如果可能的话。

Answer 1

试试这个：

select sum(value) 
  from TAB 
 where col1=12 and col2=18
 group by TimeStamp
 order by TimeStamp desc
 limit 1