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ORACLE之常用FAQ V1.0


  第一部分、SQL&PL/SQL
  [Q]怎么样查询特殊字符,如通配符%与_
  [A]select * from table where name like 'A\_%' escape '\'
  
  [Q]如何插入单引号到数据库表中
  [A]可以用ASCII码处理,其它特殊字符如&也一样,如
  insert into t values('i'||chr(39)||'m'); -- chr(39)代表字符'
  或者用两个单引号表示一个
  or insert into t values('I''m'); -- 两个''可以表示一个'
  
  [Q]怎样设置事务一致性
  [A]set transaction [isolation level] read committed; 默认语句级一致性
  set transaction [isolation level] serializable;
  read only; 事务级一致性
  
  [Q]怎么样利用游标更新数据
  [A]cursor c1 is
  select * from tablename
  where name is null for update [of column]
  ……
  update tablename set column = ……
  where current of c1;
  
  [Q]怎样自定义异常
  [A] pragma_exception_init(exception_name,error_number);
  如果立即抛出异常
  raise_application_error(error_number,error_msg,true|false);
  其中number从-20000到-20999,错误信息最大2048B
  异常变量
  SQLCODE 错误代码
  SQLERRM 错误信息
  
  [Q]十进制与十六进制的转换
  [A]8i以上版本:
  to_char(100,'XX')
  to_number('4D','XX')
  8i以下的进制之间的转换参考如下脚本
  create or replace function to_base( p_dec in number, p_base in number )
  return varchar2
  is
  l_str varchar2(255) default NULL;
  l_num number default p_dec;
  l_hex varchar2(16) default '0123456789ABCDEF';
  begin
  if ( p_dec is null or p_base is null ) then
  return null;
  end if;
  if ( trunc(p_dec) <> p_dec OR p_dec < 0 ) then
  raise PROGRAM_ERROR;
  end if;
  loop
  l_str := substr( l_hex, mod(l_num,p_base)+1, 1 ) || l_str;
  l_num := trunc( l_num/p_base );
  exit when ( l_num = 0 );
  end loop;
  return l_str;
  end to_base;
  /
  create or replace function to_dec
  ( p_str in varchar2,
  p_from_base in number default 16 ) return number
  is
  l_num number default 0;
  l_hex varchar2(16) default '0123456789ABCDEF';
  begin
  if ( p_str is null or p_from_base is null ) then
  return null;
  end if;
  for i in 1 .. length(p_str) loop
  l_num := l_num * p_from_base + instr(l_hex,upper(substr(p_str,i,1)))-1;
  end loop;
  return l_num;
  end to_dec;
  /
  
  [Q]能不能介绍SYS_CONTEXT的详细用法
  [A]利用以下的查询,你就明白了
  select
  SYS_CONTEXT('USERENV','TERMINAL') terminal,
  SYS_CONTEXT('USERENV','LANGUAGE') language,
  SYS_CONTEXT('USERENV','SESSIONID') sessionid,
  SYS_CONTEXT('USERENV','INSTANCE') instance,
  SYS_CONTEXT('USERENV','ENTRYID') entryid,
  SYS_CONTEXT('USERENV','ISDBA') isdba,
  SYS_CONTEXT('USERENV','NLS_TERRITORY') nls_territory,
  SYS_CONTEXT('USERENV','NLS_CURRENCY') nls_currency,
  SYS_CONTEXT('USERENV','NLS_CALENDAR') nls_calendar,
  SYS_CONTEXT('USERENV','NLS_DATE_FORMAT') nls_date_format,
  SYS_CONTEXT('USERENV','NLS_DATE_LANGUAGE') nls_date_language,
  SYS_CONTEXT('USERENV','NLS_SORT') nls_sort,
  SYS_CONTEXT('USERENV','CURRENT_USER') current_user,
  SYS_CONTEXT('USERENV','CURRENT_USERID') current_userid,
  SYS_CONTEXT('USERENV','SESSION_USER') session_user,
  SYS_CONTEXT('USERENV','SESSION_USERID') session_userid,
  SYS_CONTEXT('USERENV','PROXY_USER') proxy_user,
  SYS_CONTEXT('USERENV','PROXY_USERID') proxy_userid,
  SYS_CONTEXT('USERENV','DB_DOMAIN') db_domain,
  SYS_CONTEXT('USERENV','DB_NAME') db_name,
  SYS_CONTEXT('USERENV','HOST') host,
  SYS_CONTEXT('USERENV','OS_USER') os_user,
  SYS_CONTEXT('USERENV','EXTERNAL_NAME') external_name,
  SYS_CONTEXT('USERENV','IP_ADDRESS') ip_address,
  SYS_CONTEXT('USERENV','NETWORK_PROTOCOL') network_protocol,
  SYS_CONTEXT('USERENV','BG_JOB_ID') bg_job_id,
  SYS_CONTEXT('USERENV','FG_JOB_ID') fg_job_id,
  SYS_CONTEXT('USERENV','AUTHENTICATION_TYPE') authentication_type,
  SYS_CONTEXT('USERENV','AUTHENTICATION_DATA') authentication_data
  from dual
  
  [Q]怎么获得今天是星期几,还关于其它日期函数用法
  [A]可以用to_char来解决,如
  select to_char(to_date('2002-08-26','yyyy-mm-dd'),'day') from dual;
  在获取之前可以设置日期语言,如
  ALTER SESSION SET NLS_DATE_LANGUAGE='AMERICAN';
  还可以在函数中指定
  select to_char(to_date('2002-08-26','yyyy-mm-dd'),'day','NLS_DATE_LANGUAGE = American') from dual;
  其它更多用法,可以参考to_char与to_date函数
  如获得完整的时间格式
  select to_char(sysdate,'yyyy-mm-dd hh24:mi:ss') from dual;
  随便介绍几个其它函数的用法:
  本月的天数
  SELECT to_char(last_day(SYSDATE),'dd') days FROM dual
  今年的天数
  select add_months(trunc(sysdate,'year'), 12) - trunc(sysdate,'year') from dual
  下个星期一的日期
  SELECT Next_day(SYSDATE,'monday') FROM dual
  
  [Q]随机抽取前N条记录的问题
  [A]8i以上版本
  select * from (select * from tablename order by sys_guid()) where rownum < N;
  select * from (select * from tablename order by dbms_random.value) where rownum< N;
  注:dbms_random包需要手工安装,位于$ORACLE_HOME/rdbms/admin/dbmsrand.sql
  dbms_random.value(100,200)可以产生100到200范围的随机数
  
  [Q]抽取从N行到M行的记录,如从20行到30行的记录
  [A]select * from (select rownum id,t.* from table where ……
  and rownum <= 30) where id > 20;
  
  [Q]怎么样抽取重复记录
  [A]select * from table t1 where where t1.rowed !=
  (select max(rowed) from table t2
  where t1.id=t2.id and t1.name=t2.name)
  或者
  select count(*), t.col_a,t.col_b from table t
  group by col_a,col_b
  having count(*)>1
  如果想删除重复记录,可以把第一个语句的select替换为delete
  
  [Q]怎么样设置自治事务
  [A]8i以上版本,不影响主事务
  pragma autonomous_transaction;
  ……
  commit|rollback;
  
  [Q]怎么样在过程中暂停指定时间
  [A]DBMS_LOCK包的sleep过程
  如:dbms_lock.sleep(5);表示暂停5秒。
  
  [Q]怎么样快速计算事务的时间与日志量
  [A]可以采用类似如下的脚本
  DECLARE
  start_time NUMBER;
  end_time NUMBER;
  start_redo_size NUMBER;
  end_redo_size NUMBER;
  BEGIN
  start_time := dbms_utility.get_time;
  SELECT VALUE INTO start_redo_size FROM v$mystat m,v$statname s
  WHERE m.STATISTIC#=s.STATISTIC#
  AND s.NAME='redo size';
  --transaction start
  INSERT INTO t1
  SELECT * FROM All_Objects;
  --other dml statement
  COMMIT;
  end_time := dbms_utility.get_time;
  SELECT VALUE INTO end_redo_size FROM v$mystat m,v$statname s
  WHERE m.STATISTIC#=s.STATISTIC#
  AND s.NAME='redo size';
  dbms_output.put_line('Escape Time:'||to_char(end_time-start_time)||' centiseconds');
  dbms_output.put_line('Redo Size:'||to_char(end_redo_size-start_redo_size)||' bytes');
  END;
  
  [Q]怎样创建临时表
  [A]8i以上版本
  create global temporary tablename(column list)
  on commit preserve rows; --提交保留数据 会话临时表
  on commit delete rows; --提交删除数据 事务临时表
  临时表是相对于会话的,别的会话看不到该会话的数据。
  
  [Q]怎么样在PL/SQL中执行DDL语句
  [A]1、8i以下版本dbms_sql包
  2、8i以上版本还可以用
  execute immediate sql;
  dbms_utility.exec_ddl_statement('sql');
  
  [Q]怎么样获取IP地址
  [A]服务器(817以上):utl_inaddr.get_host_address
  客户端:sys_context('userenv','ip_address')
  
  [Q]怎么样加密存储过程
  [A]用wrap命令,如(假定你的存储过程保存为a.sql)
  wrap iname=a.sql
  PL/SQL Wrapper: Release 8.1.7.0.0 - Production on Tu
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