If you want to retry the data from more then one table 
connected with common key , we will go for joins (Inner 
joines and outer joins).

1. First we will create an internal table wih fields.
example.
tables: mara.
data:s_matnr for mara-matnr.
data:Begin of itab occurs 0,
   MATNR TYPE MATNR, "FROM MARA TABLE
   ERSDA TYPE ERSDA, "FROM MARA TABLE
   MAKTX TYPE MAKTX, "FROM MAKT TABLE
end of itab.

2. write select statment.
    select a~matnr
           a~ersda
           b~maktx
           from makt inner join  mara
           on a~matnr = b~matnr
           into table itab where a~matnr in s_matnr.