为什么我不能从MySQL的子查询中选择一列？

Question

I have the following data:

http://i.imgur.com/e4d8M8V.png?1

I run the following MySQL code

select distinct i.InstructorID, i.Salary
from Instructor i
where (i.InstructorID NOT IN (select o.InstructorID from Offering o));

Which gives the desired output here:

http://i.imgur.com/rkFKseX.png?1

How could I get just the salaries from this query?

I've tried

$MySQL:>select (i.Salary)
from (select distinct i.InstructorID, i.Salary
from Instructor i
where (i.InstructorID NOT IN (select o.InstructorID from Offering o)));

as well as trying to change the first select parameter to i1.Salary or just simply (Salary), but no matter what I do I just get a syntax error

SQLException: com.mysql.jdbc.exceptions.MySQLSyntaxErrorExceptio

Answer 1

In MySQL, you need a table alias after any subquery. So the following should work:

select t.Salary
from (select distinct i.InstructorID, i.Salary
      from Instructor i
      where (i.InstructorID NOT IN (select o.InstructorID from Offering o))
     ) t;

Note the t . This is a name for the subquery and is required by MySQL. The name "t" is arbitrary. You can give it any valid name.