mysql - Whats wrong with my nested subquery? -

so i'm solving interactive tutorial http://www.sqlzoo.net/wiki/select_from_nobel_tutorial bonus part doesn't have solution.

here's question: in years physics prize awarded no chemistry prize.

select yr nobel subject = 'physics' , yr not in (select yr nobel subject = 'literature') 

i got output

1943 1935 1918 1914 

when tutorial said answer is

1933 1924 1919 1917 

i don't understand why solution wrong

edit: saw careless mistake 'literature' should 'chemistry' still seems invalid

there 2 errors in query:

• you mistyped chemistry (your query says literature instead)
• you did not ask distinct results

here modified query:

select distinct yr nobel subject = 'physics' , yr not in (select yr nobel subject = 'chemistry') 

distinct important, because in 1933 physics prize has been awarded multiple winners - namely, dirac , schrödinger. these 2 rows table result in 2 entries 1933 in output, not want.