SY fields

What is SY-TABIX AND SY-INDEX.

LOOP AT ITABLE1.

WRITE : / ITABLE1-MATNR,SY-INDEX,SY-TABIX.

ENDLOOP.

The above codes displays 0 in sy-index place and 1,2,3...last record number in sy-tabix place

How to find out total number of records in a database?

Thanks in advance