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1.ɾ³ý±í
  select 'drop table ' || table_name || ' purge;'
  from user_tables
  where length(table_name) <= 4;
    ɾ³ý´øÔ¼ÊøµÄ±í
    Drop table ±íÃû cascade  constraints;
2.²éѯview&ͬÒå´Ê
   --˵Ã÷£º¿ÉÒÔ¸ù¾ÝÊÓͼµÄtext_lengthÖµÉ趨set long µÄ´óС
   set long 2000;               
   select * from user_views where view_name='MY_VIEW_NAME'; 
   select * from all_views where view_name='MY_VIEW_NAME';
   select * from user_synonyms;
3.ÁÙʱ±í
    create global temporary table xay_temp as select * from xay;
                on commit preserve rows/on commit delete rows
        ÔÚOracleÖУ¬¿ÉÒÔ´´½¨ÒÔÏÂÁ½ÖÖÁÙʱ±í:
   a »á»°ÌØÓеÄÁÙʱ±í:
        create global temporary table () on commit preserve rows;
        »á»°Ö¸¶¨£¬µ±ÖжϻỰʱORACLE½«½Ø¶Ï±í
   b ÊÂÎñÌØÓеÄÁÙʱ±í:
        create global temporary table () on commit delete rows;
        ÊÂÎñÖ¸¶¨,ÿ´ÎÌá½»ºóORACLE½«½Ø¶Ï±í£¨É¾³ýÈ«²¿ÐУ©
   c ˵Ã÷
       ÁÙʱ±íÖ»ÔÚµ±Ç°Á¬½ÓÄÚÓÐЧ
¡¡    ÁÙʱ±í²»½¨Á¢Ë÷Òý,ËùÒÔÈç¹ûÊý¾ÝÁ¿±È½Ï´ó»ò½øÐжà´Î²éѯʱ,²»ÍƼöʹÓÃ
¡¡    Êý¾Ý´¦Àí±È½Ï¸´ÔÓµÄʱºòʱ±í¿ì,·´Ö®ÊÓͼ¿ìµã
4.Ìî¼Ó×¢ÊÍ
    comment on table ±íÃû is  '×¢ÊÍ';
    comment on column ±íÃû.ÁÐÃû is '×¢ÊÍ';
5. ROWNUM
    °´É趨ÅÅÐòµÄÐеÄÐòºÅ
    SELECT * from emp WHERE ROWNUM < 10 ;
6. ROWID
    ·µ»ØÐеÄÎïÀíµØÖ·
    SELECT ROWID, ename from emp  WHERE deptno = 20 ;
7. ¸´ÖƱ