Some problems and solutions in the compilation of Pl/sql program

Program | solve | problem
1. In Pl/sql, the conditions in the ORDER BY clause can use the variable!

DECLARE
V_orderbystr VARCHAR2 (30);
V_userid VARCHAR2 (30);
V_username VARCHAR2 (30);
V_gender number;
V_rownum number;
TYPE Tcur is REF CURSOR;
Results tcur;
BEGIN
v_rownum:=0;
v_orderbystr:= ' username ';
OPEN results for select Userid,username,gender from
(select RowNum as Rowno, a.* from
(SELECT * from Home_user ORDER by V_orderbystr) a
where rownum<10)
where rowno>=1;
LOOP
FETCH results into V_userid,v_username,v_gender;
EXIT when Results%notfound;
Dbms_output.put_line (v_userid| | ' '|| v_username| | ' '|| V_gender);
v_rownum:=v_rownum+1;
End LOOP;
Close results;
Dbms_output.put_line (V_rownum);
End;

2, while writing dynamic SQL stored procedures, found in the use clause, found that the table name can not be used as a placeholder parameter! And can only be replaced by the method below, that is, directly linked to the table name and string, other variables can be replaced by the placeholder;
V_sqlstr:= ' SELECT * FROM (select RowNum rowno,t.* from '
||' (SELECT SequenceID msgid,themeid,id,topic,hits,replys,nickname '
||' From ' | | tablename| | ' where themeid=:a2 order By:a3) t where Rownum<:a4 '
||') WHERE Rowno>=:a5 ';
Dbms_output.put_line (V_SQLSTR);
OPEN o_results for V_sqlstr USING P_themeid,v_orderbystr,v_endrow,v_startrow;

3, in doing some paging query, the use of pseudo-column rownum, found that rownum can only be used for rownum<10 and other applications, but not rownum>10; in the example of the implementation of the same time paging function;

4, use the existing table to create a new table, and copy the table structure of the source table:
CREATE TABLE newtable as (SELECT * oldtable where 1=2)