1.parallel execution 并行执行
2.strength优点 weakness缺点 seed潜能 virtue 品德 competence能力
3. variable scn numberexec :scn:=dbms_flashback.get_system_change_number;
select * from tablename as of scn :scn;
select * from tablename as of timestamp sysdate-1/1440;
select timestamp_to_scn(to_date('2010-01-01 10:10:10','yyyy-mm-dd hh24:mi:ss')) from dual；
alter table enable row movement; /*this operation will cause a new rowid;*/
flashback table tablename to scn :scn;
function index: create index t_index on t(nvl(id,-1));
4.better not to create temporary table in procedure:
because DDL statement will commit transaction;
must dynamicly using the temporary table in procedure;
Its performance is worse than static statement.