我可以使用2个不同列中的信息来指定UPDATE查询中更新信息的位置吗？

Consider this table:

Email | Message | Votes
------+---------+-------
Email1| Msg1    | 2
------+---------+-------
Email2| Msg2    | 1
------+---------+-------
Email3| Msg2    | 3

Now, I want to update the 3rd cell under Votes column using following query:

UPDATE tablename SET Votes=4 WHERE Message=Msg2

But the problem is that it will update the both cells under Votes, where Msg2 is present. But I want to update the cell where Email=Email3 and Message=Msg2.

Can it be done using UPDATE query?

Use multiple condtitions and join them with AND:

UPDATE tablename 
SET Votes = 4 
WHERE Message = 'Msg2'
  AND Email   = 'Email3';

or using row-constructor:

UPDATE tablename 
SET Votes = 4 
WHERE (Message, Email) = ('Msg2','Email3');

SqlFiddleDemo

EDIT:

I tried but it didn't work. It didn't update anything

So you have different data than you provided. Probably whitespaces. Try:

UPDATE tablename 
SET Votes = 4 
WHERE TRIM(Message) = 'Msg2'
  AND TRIM(Email)   = 'Email3';