title: SOQL in apex - Getting unmatched results from two object types
body: <p>Does any one know how to write an SOQL in apex for below scenario</p>
  
  <p>" There are two object say "Countries" and "MappedCountries" where Countries object  will have a complete list of Countries and MappedCountries will only have a few Countries(it is like subset of Countries object ).</p>
  
  <p>Now I want an SOQL apex function like " I want entries in Countries object type which are not matched in MappedCountries object type".</p>
  
  <p>For eg : Countries Object type consists of IND AUS NZ ENG and MappedCountries object type consists of NZ AUS then the query should obtain the unmatched result from two object types as IND ENG.</p>
  
  <p>Help me regarding this.</p>