INSERT INTO <table> SELECT <target>, <other columns> FROM <table> WHERE mandt = <source>

insert into employees select 'B',employee,name from employees where mandt='A';

create or replace procedure prc_test as 

cursor cur_DELETE is
  select UPPER(TABELLENNAME) as TABELLE
  from TBLMANDTSchema 
  where MITMANDT='X'
  order by RHFLG desc;
  
cursor cur_TABLES is
  select UPPER(TABELLENNAME) AS TABELLE
  from TBLMANDTSCHEMA 
  where MITMANDT='X'
  order by RHFLG asc;  
  
  wa_col   user_tab_cols%ROWTYPE;  
  wa_table cur_DELETE%ROWTYPE;
  
  v_delete varchar2(255);
  v_select varchar2(255);
  v_cols   varchar2(255);
  
  v_qmandt char(1);
  v_zmandt char(1);
  
BEGIN

  v_qmandt := '0';  --source client
  v_zmandt := '3';  --target client
  
  dbms_output.put_line('Start deleting:');
  
  /* DELETE ENTRIES IN TARGET CLIENT */
  for wa_table in cur_DELETE
  loop
    v_delete := 'DELETE FROM ' || wa_table.TABELLE || ' WHERE MANDT= :m';
    dbms_output.put_line( v_delete );
    execute immediate v_delete using v_zmandt;
    commit;      
  end loop; 
  
  dbms_output.put_line('Start copying:');
  for wa_table in cur_TABLES
    loop
  
        /* CONCATENATE COLUMNS OTHER THAN 'MANDT' */
        declare
        cursor cur_TABELLEN_SP is
           SELECT * FROM USER_TAB_COLS WHERE TABLE_NAME = wa_table.TABELLE
           AND COLUMN_NAME <> 'MANDT' 
           ORDER BY COLUMN_ID;       
        begin
            v_cols := '';
            for wa_col in cur_TABELLEN_sp
            loop
              --dbms_output.put_line( wa_col.column_name );
              v_cols := v_cols || wa_col.column_name || ', ';
            end loop;
        end;
        v_cols := substr(v_cols, 0, LENGTH(v_cols)-2);
        dbms_output.put_line( 'Table ' || wa_table.TABELLE || ' has columns: ' || v_cols);
          
        v_SELECT := 'INSERT INTO ' || wa_table.TABELLE || ' SELECT :t , ' || v_cols || ' FROM ' ||  wa_table.TABELLE || ' WHERE MANDT = :s';
        execute immediate v_select using v_zmandt, v_qmandt;
        commit;
     
    end loop;

end prc_test;