title: SQL How to insert null value
body: <p>I want to insert data into one table from another table.  In some of the columns I don't have data, so I want to set column to null.  I don't know how I should do this? </p>
  
  <p>This is the SQL:</p>
  
  <pre><code>INSERT INTO _21Appoint(
     PCUCODE,PID,SEQ,
     DATE_SERV,APDATE,
     APTYPE,APDIAG,D_UPDATE,CID
  ) SELECT (
     NULL,NULL,NULL,
     treatment_date,appointment_date,
     typeap_id,appointment_id,NULL,patient_id
  ) FROM cmu_treatment,cmu_appointment
    WHERE cmu_treatment.treatment_id LIKE cmu_appointment.treatment_id;
  </code></pre>