第一部分、SQL&PL/SQL
[Q]怎么样查询非凡字符,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,其它非凡字符如&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);
假如立即抛出异常
raise_application_error(error_number,error_msg,truefalse);
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的具体用法
[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') fromdual;
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$Oracle_HOME/rdbms/admin/dbmsrand.sql
dbms_random.value(100,200)可以产生100到200范围的随机数
[Q]抽取从N行到M行的记录,如从20行到30行的记录
[A]select * from (select rownum id,t.* from table where ……
and rownum <= 30) where id > 20;
[Q]怎么样抽取重复记录
[A]select * from table t1 where where t1.rowed !=
(select max(rowed) from table t2
where t1.id=t2.id and t1.name=t2.name)
或者
select count(*), t.col_a,t.col_b from table t
group by col_a,col_b
having count(*)>1
假如想删除重复记录,可以把第一个语句的select替换为delete
[Q]怎么样设置自治事务
[A]8i以上版本,不影响主事务
pragma autonomous_transaction;
……
commitrollback;
[Q]怎么样在过程中暂停指定时间
[A]DBMS_LOCK包的sleep过程
如:dbms_lock.sleep(5);表示暂停5秒。
[Q]怎么样快速计算事务的时间与日志量
[A]可以采用类似如下的脚本
DECLARE
start_time NUMBER;
end_time NUMBER;
start_redo_size NUMBER;
end_redo_size NUMBER;
BEGIN
start_time := dbms_utility.get_time;
SELECT VALUE INTO start_redo_size FROM v$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 Tue Nov 27 22:26:48 2001
Copyright (c) Oracle Corporation 1993, 2000.All Rights Reserved.
Processing a.sql to a.plb
提示a.sql转换为a.plb,这就是加密了的脚本,执行a.plb即可生成加密了的存储过程
[Q]怎么样在ORACLE中定时运行存储过程
[A]可以利用dbms_job包来定时运行作业,如执行存储过程,一个简单的例子,提交一个作业:
VARIABLE jobno number;
BEGIN
DBMS_JOB.SUBMIT(:jobno, 'ur_procedure;',SYSDATE,'SYSDATE + 1');
commit;
END;
之后,就可以用以下语句查询已经提交的作业
select * from user_jobs;
[Q]怎么样从数据库中获得毫秒
[A]9i以上版本,有一个timestamp类型获得毫秒,如
SQL>select to_char(systimestamp,'yyyy-mm-dd hh24:mi:ssxff') time1,
to_char(current_timestamp) time2 from dual;
TIME1 TIME2
----------------------------- ----------------------------------------------------------------
2003-10-24 10:48:45.65600024-OCT-03 10.48.45.656000 AM +08:00
可以看到,毫秒在to_char中对应的是FF。
8i以上版本可以创建一个如下的Java函数
SQL>create or replace and compile
java source
named "MyTimestamp"
as
import java.lang.String;
import java.sql.Timestamp;
public class MyTimestamp
{
public static String getTimestamp()
{
return(new Timestamp(System.currentTimeMillis())).toString();
}
};
SQL>java created.
注:注重java的语法,注重大小写
SQL>create or replace function my_timestamp return varchar2
as language java
name 'MyTimestamp.getTimestamp() return java.lang.String';
/
SQL>function created.
SQL>select my_timestamp,to_char(sysdate,'yyyy-mm-dd hh24:mi:ss') ORACLE_TIME from dual;
MY_TIMESTAMP ORACLE_TIME
------------------------ -------------------
2003-03-17 19:15:59.6882003-03-17 19:15:59
假如只想获得1/100秒(hsecs),还可以利用dbms_utility.get_time
[Q]假如存在就更新,不存在就插入可以用一个语句实现吗
[A]9i已经支持了,是Merge,但是只支持select子查询,
假如是单条数据记录,可以写作select …… from dual的子查询。
语法为:
MERGE INTO table
USING data_source
ON (condition)
WHEN MATCHED THEN update_clause
WHEN NOT MATCHED THEN insert_clause;
如
MERGE INTO course c
USING (SELECT course_name, period,
course_hours
FROM course_updates) cu
ON (c.course_name = cu.course_name
AND c.period = cu.period)
WHEN MATCHED THEN
UPDATE
SET c.course_hours = cu.course_hours
WHEN NOT MATCHED THEN
INSERT (c.course_name, c.period,
c.course_hours)
VALUES (cu.course_name, cu.period,
cu.course_hours);
[Q]怎么实现左联,右联与外联
[A]在9i以前可以这么写:
左联:
select a.id,a.name,b.address from a,b
where a.id=b.id(+)
右联:
select a.id,a.name,b.address from a,b
where a.id(+)=b.id
外联
SELECT a.id,a.name,b.address
FROM a,b
WHERE a.id = b.id(+)
UNION
SELECT b.id,'' name,b.address
FROM b
WHERE NOT EXISTS (
SELECT * FROM a
WHERE a.id = b.id);
在9i以上,已经开始支持SQL99标准,所以,以上语句可以写成:
默认内部联结:
select a.id,a.name,b.address,c.subject
from (a inner join b on a.id=b.id)
inner join c on b.name = c.name
where other_clause
左联
select a.id,a.name,b.address
from a left outer join b on a.id=b.id
where other_clause
右联
select a.id,a.name,b.address
from a right outer join b on a.id=b.id
where other_clause
外联
select a.id,a.name,b.address
from a full outer join b on a.id=b.id
where other_clause
or
select a.id,a.name,b.address
from a full outer join b using (id)
where other_clause
[Q]怎么实现一条记录根据条件多表插入
[A]9i以上可以通过Insert all语句完成,仅仅是一个语句,如:
INSERT ALL
WHEN (id=1) THEN
INTO table_1 (id, name)
values(id,name)
WHEN (id=2) THEN
INTO table_2 (id, name)
values(id,name)
ELSE
INTO table_other (id, name)
values(id, name)
SELECT id,name
FROM a;
假如没有条件的话,则完成每个表的插入,如
INSERT ALL
INTO table_1 (id, name)
values(id,name)
INTO table_2 (id, name)
values(id,name)
INTO table_other (id, name)
values(id, name)
SELECT id,name
FROM a;
[Q]如何实现行列转换
[A]1、固定列数的行列转换
如
studentsubject grade
---------------------------
student1语文 80
student1数学 70
student1英语 60
student2语文 90
student2数学 80
student2 英语 100
……
转换为
语文数学英语
student1 8070 60
student2 9080 100
……
语句如下:
select student,sum(decode(subject,'语文', grade,null)) "语文",
sum(decode(subject,'数学', grade,null)) "数学",
sum(decode(subject,'英语', grade,null)) "英语"
from table
group by student
2、不定列行列转换
如
c1 c2
--------------
1我
1是
1谁
2知
2道
3不
……
转换为
1 我是谁
2 知道
3 不
这一类型的转换必须借助于PL/SQL来完成,这里给一个例子
CREATE OR REPLACE FUNCTION get_c2(tmp_c1 NUMBER)
RETURN VARCHAR2
IS
Col_c2 VARCHAR2(4000);
BEGIN
FOR cur IN (SELECT c2 FROM t WHERE c1=tmp_c1) LOOP
Col_c2 := Col_c2cur.c2;
END LOOP;
Col_c2 := rtrim(Col_c2,1);
RETURN Col_c2;
END;
/
SQL> select distinct c1 ,get_c2(c1) cc2 from table;即可
[Q]怎么样实现分组取前N条记录
[A]8i以上版本,利用分析函数
如获取每个部门薪水前三名的员工或每个班成绩前三名的学生。
Select * from
(select depno,ename,sal,row_number() over (partition by depno
order by sal desc) rn
from emp)
where rn<=3
[Q]怎么样把相邻记录合并到一条记录
[A]8i以上版本,分析函数lag与lead可以提取后一条或前一天记录到本记录。
Select deptno,ename,hiredate,lag(hiredate,1,null) over
(partition by deptno order by hiredate,ename) last_hire
from emp
order by depno,hiredate
[Q]如何取得一列中第N大的值?
[A]select * from
(select t.*,dense_rank() over (order by t2 desc) rank from t)
where rank = [$N]
[Q]怎么样把查询内容输出到文本
[A]用spool如
如sqlplus –s" / as sysdba" <
set heading off
set feedback off
spool temp.txt
select * from tab;
dbms_output.put_line(‘test’);
spool off
exit
EOF
[Q] 如何在SQL*PLUS环境中执行OS命令?
[A] 比如进入了SQLPLUS,启动了数据库,忽然想起监听还没有启动,此时不用退出SQLPLUS,也不用另外起一个命令行窗口,直接输入:
SQL> host lsntctl start
或者unix/Linux平台下
SQL>!
windows平台下
SQL>$
总结:HOST 可以直接执行OS命令。
备注:cd命令无法正确执行。
[Q]怎么设置存储过程的调用者权限
[A]普通存储过程都是所有者权限,假如想设置调用者权限,请参考如下语句
create or replace
procedure ……()
AUTHID CURRENT_USER
As
begin
……
end;