If IsNull({DECL_INV_ITEM_I.DECLEAR_NO}) Or Trim({DECL_INV_ITEM_I.DECLEAR_NO}) = "" Then "0" Else CStr({DECL_INV_ITEM_I.EX_RATE},5,',')
CSTR({number_field}, 0, ''),第一个是数字字段;第二个是保留的小数位,0是整数;第三个是千分位分隔字符。