oralce個人備忘

1.壓縮存儲數據時，create table 加上COMPRESS選項，向表插入數據時，要排序插入，這樣相同數據就存放一次，節約空間提高I/O效率。弊端，經常UPDATE的話會影響DML性能

2.表字段的unused和查看

alter table t1 set unused column column_name

select obj#,col#,name from sys.col$
where obj# = 'select object_id from dba_objects where object_name = 'T1';
alter table t1 drop unused columns;

3.使用UTL_FILE包導出表爲文本，適用大表導出

declare
v_file utl_file.file_type;
begin
v_file:=utl_file.fopen('/u01','output.txt','w');
utl_file.putf(v_file,'output date: %s\n',sysdate);
utl_file.new_line(v_file);
for i in(select * from scott.t1) loop
utl_file.putf(v_file,'%s,%s,%s\n',i.ename,i.empno,i.sal);
end loop;
utl_file.fclose(v_file);
end;
/

 4. v$transaction 跟 v$session 使用v$transaction.addr = v$session.taddr關聯