动态执行sql,返回一个值

 function dyn_sql(p_sql in varchar2) return varchar2 is
 c integer;
 result varchar2(4000);
 l_temp number;
 begin
 c := dbms_sql.open_cursor;
 dbms_sql.parse(c, p_sql, dbms_sql.native);
 if upper(p_sql) like 'SELECT%' then
 dbms_sql.define_column(c, 1, result, 4000);
 l_temp := dbms_sql.execute_and_fetch(c);
 if l_temp > 0 then
 dbms_sql.column_value(c, 1, result);
 else
 result := null;
 end if;
 else
 l_temp := dbms_sql.execute(c);
 result := null;
 end if;
 dbms_sql.close_cursor(c);
 return result;
 end dyn_sql;