How does sy-tabix affect by binary search transforming no fields?

Question

1 report ztx1110.
     2 data: begin of it occurs 3,
     3           f1(2) type n,
     4           f2    type i,
     5           f3(2) type c,
     6           f4    type p,
     7           end of it.
     8
     9   it-f1 = '40'. it-f3 = 'DD'. it-f2 = it-f4 = 4. append it.
    10  it-f1 = '20'. it-f3 = 'BB'. it-f2 = it-f4 = 2. append it.
    11
    12 sort it by f1.
    13 do 5 times.
    14     it-f1 = sy-index * 10.
    15     it-f3 = 'XX'.
    16     it-f2 = it-f4 = sy-index.
    17     read table it
    18         with key f1 = it-f1
    19         binary search
    20         transporting no fields.
    21     if sy-subrc <> 0.
    22         insert it index sy-tabix.
    23         endif.
    24     enddo.
    25
    26 loop at it.
    27     write: / it-f1, it-f2, it-f3, it-f4.
    28     endloop.
in this program changing value of sy-tabix as such sy-index.
means in it's first loop it's value is 1, on second loop it's 2, and so on up to 5.
okay that is due to binary search.
but why binary search affecting this system variable?

Answer 1

Hi Vinay,
It is simple.
This depends on your select query. 
CASE 1: If you use select ..into table.....,  then there wil be nothing in your header ls_vbap. Now if you execute READ stmt..you will get nothing.
CASE 2: If you use Select..... into ls_vbap.....append ls_vbap....clear ls_vbap.....endselect.   In this case also the output of READ will be nothing because you are clearing header.  So while READ stmt you are comparing ls_vbap-vbeln and ls_vbap-posnr , as nothing in it you will get nothing
CASE 3: If you use case 2 without CLEAR stmt then always you will get the index of the last fetched record...i.e., the last record of the internal table before sorting..
I think it is helpful for you....if you are not clear just reply me