title: Syntax error "field ITAB unknown" in APPEND wa TO itab
body: <p>I am trying to add a new record to my internal table and this code is giving me an error, but I am doing exactly the same thing as in my SAP book. What am I doing wrong?</p>
  
  <pre><code>TYPES : BEGIN OF personel_bilgileri,
    Ad TYPE c LENGTH 20,
    Soyad TYPE c LENGTH 20,
    Telefon_no Type n LENGTH 12,
    END OF personel_bilgileri.
  
  TYPES personel_bilgi_tablo_tipi TYPE STANDARD TABLE OF
  personel_bilgileri WITH NON-UNIQUE KEY ad soyad.
  
  DATA : personel_bilgi_kaydi TYPE personel_bilgileri,
         personel_bilgi_tablosu TYPE personel_bilgi_tablo_tipi.
  
  personel_bilgi_kaydi-ad = 'Murat'.
  personel_bilgi_kaydi-soyad = 'Sahin'.
  personel_bilgi_kaydi-telefon_no = '5556677'.
  
  APPEND personel_bilgi_kaydi TO personel_bilgileri.
  
  personel_bilgi_kaydi-ad  = 'Ayse'.
  personel_bilgi_kaydi-soyad = 'Bil'.
  personel_bilgi_kaydi-telefon_no = '5556611'.
  
  APPEND personel_bilgi_kaydi TO personel_bilgileri.
  
  personel_bilgi_kaydi-ad = 'Mehmet'.
  personel_bilgi_kaydi-soyad = 'Kalan'.
  personel_bilgi_kaydi-telefon_no = '5556622'.
  
  APPEND personel_bilgi_kaydi TO personel_bilgileri.
  </code></pre>
  
  <p>Actually, I don't know which adding record method I should use. I mean there is too many ways to do this operation. Which method will be the true one?</p>
  
  <p>I am getting this error:</p>
  
  <pre><code>The field Personel_bilgileri is unknown, but there are following fields similar names...
  </code></pre>
  
  <p>Moreover, I can do this with LOOP AT, but I didn't understand the usage of LOOP AT. What does it do?</p>