将SQL查询转换为LINQ表达式

Question

I want to select all Systems that are not in table Process_Systems by incoming process_Id in method, i have writen SQL but now i need LINQ.. Please help me How to convert SQL query like this to LINQ:

  SELECT   *
   FROM     Systems
     WHERE    id NOT IN (
       SELECT systemid
        FROM   Process_Systems
       WHERE  processId = 4
     );

or this one (these are equal)

  SELECT   Systems.*
  FROM     Systems LEFT JOIN Process_Systems ps
    ON ps.systemId = Systems.id
  AND ps.processId = 4
  WHERE    ps.systemId IS NULL;

Answer 1

var query = from system in Systems
             where id != (from process_system in Process_Systems
                          where process_system.processId == 4
                          select process_system.systemid).First()
             select system;

Finally you'll got IEnumerable object. If I got your question.