types: begin of t1,
       a(10),
       end of t1,
       tt type table of t1.

data:
  cnt type i,
  wa type t1.
data: begin of tab occurs 0,
      n type i,
      b type tt,
      end of tab.

field-symbols:
  <fs> type tt.

cnt = 0.
do 10 times.
  cnt = cnt + 1.
  tab-n = cnt.
  do 10 times.
    wa-a = cnt.
    insert wa into table tab-b.
  enddo.
  append tab. clear tab.
enddo.

loop at tab.
  assign tab-b to <fs>.
  loop at <fs> into wa.
    write wa.
  endloop.
  write : /.
endloop.

types: begin of user_type,
        uname type uname,
        number(3) type n,
       end of user_type.

data: begin of itab occurs 0,
       bukrs type bukrs,
       users type table of user_type,
      end of itab.

data: wa_users type user_type.
field-symbols: <fw> like line of itab,
               <fw1> type user_type.

itab-bukrs = 1000.
wa_users-uname = 'IVANOV'.
wa_users-number = 101.
  append wa_users to itab-users.

  wa_users-uname = 'PETROV'.
  wa_users-number = 102.
  append wa_users to itab-users.
append itab.

end-of-selection.

*1
loop at itab assigning <fw>.
loop at <fw>-users assigning <fw1>.
  write: / <fw1>-number.
endloop.
endloop.
*2
loop at itab-users assigning <fw1>.
write: / <fw1>-uname.
*3
read table itab-users assigning <fw1> with key uname = 'PETROV'.
write: / <fw1>-number.
endloop.

t-t[] = t[].