1) 减少使用select.....endselect, but when you want to order data, still use this form.
要习惯使用以下这种写法：
select data from table into it_tab.
loop at it_tab.
select data.
modify it_tab.
endloop.
2）在LOOP.....ENDLOOP中要记得clear local variable and local internal table.
otherwise the value will be modified into the next data.
Loop at it_tab.
Clear l_text <--- 注意!!!
Select single maktx into l_text from makt where matnr = it_tab-matnr.
move l_text to it_tab-text.
Modify it_tab index sy-tabix.
Endloop.
Clear l_text <--- 注意!!!
Select single maktx into l_text from makt where matnr = it_tab-matnr.
move l_text to it_tab-text.
Modify it_tab index sy-tabix.
Endloop.
3) 注意币别的convert ： via function "currency_convert_factor "
4) select table 时，where condition must be the index or key, if not, the program will have performance issue!
5) table relation is 1:1 or 1:n?
6) select table 时， 注意前置零的问题， via funciton "convert_exit_alpha_input" & "convert_exit_alpha_output"
ex: 畫面輸入 PO: 9517
select CAUFV where aufnr eq '000000009517' (使用 9157 會找不到資料)
select CAUFV where aufnr eq '000000009517' (使用 9157 會找不到資料)
7）相同的table不要在程序中反复select，尽量使用internal table
8）不断修改增加.....