#1242: Subquery Returns more than one row

Question

I have a problem regarding mysql.

I have few tables like course, papers, students, studentspapers

Now what I want is that my query should return the result like:

It should select student name, student category from students table, students optional paper from studentspaper but I have not mentioned anything in my studentpapers table but in papers table.

Papers table have id as primary key which I have used in studentspaper as foreign key.

Now the simple query I am using is:

select
  st.name,
  s.paperid
from
  students st,
  sps s join papers
  on paperid
where
  paperid = (select p.p_id from papers p where type='optional')
  and st.course=1

I dont know what shall I do.

Its saying subquery return more than 1 row #1242

Answer 1

Your query is:

select st.name, s.paperid
from students st,
     sps s join
     papers
     on paperid
where paperid= (select p.p_id from papers p where type='optional') and st.course=1

It is missing a join between students and sps. I think you mean:

select st.name, s.paperid
from students st join
     sps s
     on st.studentid = sps.studentid join
     papers p
     on p.paperid = sps.paperid
where p.type='optional' and st.course=1

However, without seeing the structure of the tables, it is hard to say if this is the right query.

Answer 2

In this case you have to change your SQL to sth this:

select st.name, s.paperid 
from students st, sps s join papers on paperid 
where paperid in (select p.p_id from papers p where type='optional') and st.course=1

I just changed the "=" to the "in".

This should resolve your problem.