It’s very easy to get tied up in knots where performance is concerned when you’re working with internal tables – especially when they’re getting really big. In fact these problems often only arise after a few months, when the tables tend to grow as time goes by.

For example, when you’re looping two tables, one of headers and another of entries, do you do this?

LOOP AT itab1 ASSIGNING <fs1>.
   LOOP AT itab2 ASSGNING <fs2> WHERE field1 = <fs1>-field1.
   ENDLOOP.
ENDLOOP.

Did you know that for big tables this can take ages because LOOP WHERE makes a sequential reading of itab2 for each entry in itab1?

Why don’t you do this instead?

SORT itab2 BY field1.

LOOP AT itab1 ASSIGNING <fs1>.

   READ TABLE itab2 WITH KEY field1 = <fs1>-field1
      BINARY SEARCH TRANSPORTING NO FIELDS.
   CHECK SY-SUBRC = 0.
   lv_tabix = sy-tabix.

   LOOP AT itab2 FROM lv_tabix ASSIGNING <fs2>.
      IF <fs2>-field1 <> <fs1>-field1.
         EXIT.
      ENDIF.
   ENDLOOP.

ENDLOOP.

It makes all the difference in the world in terms of performance. The more data points there are in itab2 , the greater the difference.

This advantage of LOOP FROM INDEX also works if you use a SORTED TABLE instead of normal internal tables. But we’ll keep this for another article.

Thanks to Bruno Filipa for this tip.

Greetings from Abapinho.