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[转]DBCC DBREINDEX重徏索引提高SQL Server性能

Stephen — Sat, 17 May 2008 03:47:00 GMT

DBCC DBREINDEXSQL ServerSQL ServerSQL Server 1. SQL Server8KB100%SQL Server 可以通过DBCC SHOWCONTIG

2. DBCC SHOWCONTIGDBCC SHOWCONTIGDBCC REDBINDEX应用�E�序�?/span>Employee�?/span>�Q�在 SQL ServerQuery analyzeruse database_name

declare @table_id int

set @table_id=object_id('Employee')

dbcc showcontig(@table_id)

DBCC SHOWCONTIG scanning 'Employee' table...

Table: 'Employee' (1195151303); index ID: 1, database ID: 53

TABLE level scan performed.

- Pages Scanned................................: 179

- Extents Scanned..............................: 24

- Extent Switches..............................: 24

- Avg. Pages per Extent........................: 7.5

- Scan Density [Best Count:Actual Count].......: 92.00% [23:25]

- Logical Scan Fragmentation ..................: 0.56%

- Extent Scan Fragmentation ...................: 12.50%

- Avg. Bytes Free per Page.....................: 552.3

- Avg. Page Density (full).....................: 93.18%

DBCC execution completed. If DBCC printed error messages, contact your system administrator.

                                           Pages Scanned                    Extents Scanned                 Extent Switches                  DBCCAvg. Pages per Extent         Scan Density[Best Count:Actual Count]

Best CountActual CountScan Density100%Logical Scan Fragmentation   Extent Scan Fragmentation    Avg. Bytes Free per Page       Avg. Page Density (full)         Best count23 Actual Count25ordersDBCC DBREINDEX3. DBCC DBREINDEX DBCC DBREINDEX

    (    [ 'database.owner.table_name'

            [ , index_name

                [ , fillfactor ]

            ]

        ]

    )

'database.owner.table_name'

数据库、所有者和表名必须�W�合标识�W�的规则。有��x(ch��ng)��多信息，请参见��用标识符�?/span> database owner (') database.owner.table_name table_nameindex_name

索引名必��ȝ��合标识符的规则�?/span> index_name ' 'fillfactor

fillfactor fillfactor 0DBCC DBREINDEX fillfactorQuery Analyzerdbcc dbreindex('database_name.dbo.Employee','',90)

DBCC SHOWCONTIGDBCC SHOWCONTIG scanning 'Employee' table...

Table: 'Employee' (1195151303); index ID: 1, database ID: 53

TABLE level scan performed.

- Pages Scanned................................: 178

- Extents Scanned..............................: 23

- Extent Switches..............................: 22

- Avg. Pages per Extent........................: 7.7

- Scan Density [Best Count:Actual Count].......: 100.00% [23:23]

- Logical Scan Fragmentation ..................: 0.00%

- Extent Scan Fragmentation ...................: 0.00%

- Avg. Bytes Free per Page.....................: 509.5

- Avg. Page Density (full).....................: 93.70%

DBCC execution completed. If DBCC printed error messages, contact your system administrator.

Scan Denity100%******

SQL SERVERhttp://www.csdn.com.cn/database/1142.htm

unknown

Stephen 2008-05-17 11:47 发表评论

Oracle�l�验技巧集锦[ZT]

Stephen — Wed, 21 Dec 2005 03:02:00 GMT

1�Q�删除表�I�间

DROP TABLESPACE TableSpaceName [INCLUDING CONTENTS [AND DATAFILES]]
2�Q�删除用�?/FONT>

DROP USER User_Name CASCADE

3�Q�删除表的注意事��?/FONT>

在删除一个表中的全部数据�Ӟ��M��用TRUNCATE TABLE 表名;因�ؓ(f��)用DROP TABLE�Q�DELETE * FROM 表名�Ӟ��TABLESPACE表空间该表的占用�I�间�q�未释放�Q�反复几�ơDROP�Q�DELETE操作后，该TABLESPACE上百兆的�I�间��p��耗光�?ji��n)�?/FONT>

4�Q�having子句的用�?/FONT>

having子句对group by子句所��定的行�l�进行控�Ӟ��having子句条�g中只允许涉及(qi��ng)帔R��,聚组函数或group by 子句中的列�?/FONT>

5�Q�外部联�?+"的用�?/FONT>

外部联接"+"按其�?="的左�Ҏ(gu��)��双��分左联接和右联接.若不�?+"�q�算�W�的表中的一个行不直接匹配于�?+"预算�W�的表中的�Q何行,则前者的行与后者中的一个空行相匚w��q�被�q�回.若二者均不带�?�?则二者中无法匚w��的均被返�?利用外部联接"+",可以替代效率十分低下�?not in �q�算,大大提高�q�行速度.例如,下面�q�条命��o(h��)执行��h��很慢

用外联接提高表连接的查询速度

在作表连�?常用于视�?�Ӟ��怋�用以下方法来查询数据:

SELECT PAY_NO, PROJECT_NAME
FROM A
WHERE A.PAY_NO NOT IN (SELECT PAY_
NO FROM B WHERE VALUE >=120000);

---- 但是若表A�?0000条记录，表B�?0000条记录，则要用掉30分钟才能查完�Q�主要因为NOT IN要进行一条一条的比较�Q�共需�?0000*10000�ơ比较后�Q�才能得到结果。该用外联接后，可以�~�短�?分左右的旉��:

SELECT PAY_NO,PROJECT_NAME
FROM A,B
WHERE A.PAY_NO=B.PAY_NO(+)
AND B.PAY_NO IS NULL
AND B.VALUE >=12000;

6�Q�set transaction命��o(h��)的用�?/STRONG>

在执行大事务�?有时oracle�?x��)报出如下的错�?

ORA-01555:snapshot too old (rollback segment too small)

　　�q�说明oracle�l�此事务随机分配的回滚段太小�?�q�时可以为它指定一个��够大的回滚段,以确保这个事务的成功执行.例如

set transaction use rollback segment roll_abc;
delete from table_name where ...
commit;

　　回滚�D�roll_abc被指定给�q�个delete事务,commit命��o(h��)则在事务�l�束之后取消�?ji��n)回滚段的指�?

7�Q�数据库重徏应注意的问题

　　在利用import�q�行数据库重��E�中,有些视图可能�?x��)带来问�?因�ؓ(f��)�l�构输入的顺序可能造成视图的输入先于它低层�ơ表的输�?�q�样建立视图��׃��(x��)��p�|.要解册��一问题,可采取分两步走的�Ҏ(gu��)��:首先输入�l�构,然后输入数据.命��o(h��)举例如下 (uesrname:jfcl,password:hfjf,host sting:ora1,数据文�g:expdata.dmp):

imp jfcl/hfjf@ora1 file=empdata.dmp rows=N
imp jfcl/hfjf@ora1 file=empdata.dmp full=Y buffer=64000
commit=Y ignore=Y

　　�W�一条命令输入所有数据库�l�构,但无记录.�W�二�ơ输入结构和数据,64000字节提交一��?ignore=Y选项保证�W�二�ơ输入既使对象存在的情况下也能成�?

select a.empno from emp a where a.empno not in (select empno from emp1 where job=’SALE�?;

　　倘若利用外部联接,改写命��o(h��)如下:

select a.empno from emp a ,emp1 b
where a.empno=b.empno(+)
and b.empno is null
and b.job=’SALE�?

可以发现,�q�行速度明显提高.

8�Q�从已知表新建另一个表�Q?/FONT>

CREATE TABLE b
AS SELECT * (可以是表a中的几列)
FROM a
WHERE a.column = ...;

9�Q�查找、删除重复记�?

法一: 用Group by语句此查扑־�快的

select count(num), max(name) from student --查找表中num列重复的�Q�列出重复的记录敎ͼ��q�列��Z��的name属�?BR>group by num
having count(num) >1 --按num分组后找�?gu��)��中num列重复，卛_��现次数大于一��?BR>delete from student(上面Select�?

�q�样的话��把所有重复的都删除了(ji��n)�?----慎重

法二:当表比较�?例如10万条以上)�?�q�个�Ҏ(gu��)��的效率之差��o(h��)人无法忍�?需要另惛_��?

---- 执行下面SQL语句后就可以昄��所有DRAWING和DSNO相同且重复的记录

SELECT * FROM EM5_PIPE_PREFAB
WHERE ROWID!=(SELECT MAX(ROWID) FROM EM5_PIPE_PREFAB D --D相当于First,Second
WHERE EM5_PIPE_PREFAB.DRAWING=D.DRAWING AND
EM5_PIPE_PREFAB.DSNO=D.DSNO);

---- 执行下面SQL语句后就可以刪除所有DRAWING和DSNO相同且重复的记录

DELETE FROM EM5_PIPE_PREFAB
WHERE ROWID!=(SELECT MAX(ROWID) FROM EM5_PIPE_PREFAB D
WHERE EM5_PIPE_PREFAB.DRAWING=D.DRAWING AND
EM5_PIPE_PREFAB.DSNO=D.DSNO);

10�Q�返回表中[N�Q�M]条记录：(x��)

取得某列中第N大的�?

select column_name from
(select table_name.*,dense_rank() over (order by column desc) rank from table_name)
where rank = &N�Q?

　假如要返回前5条记录：(x��)

　　select * from tablename where rownum<6;(或是rownum <= 5 或是rownum != 6)

假如要返回第5-9条记录：(x��)

select * from tablename
where �?
and rownum<10
minus
select * from tablename
where �?
and rownum<5
order by name

选出�l�果后用name排序昄��l�果�?先选再排序)

注意�Q�只能用以上�W�号(<�?lt;=�?=)�?

select * from tablename where rownum != 10;�q�回的是前９条记录�?

不能用：(x��)>,>=,=,Between...and。由于rownum是一个��L��?开始的伪列�Q�Oracle 认�ؓ(f��)�q�种条�g 不成立，查不到记�?

另外�Q�这个方法更快：(x��)

select * from (
select rownum r,a from yourtable
where rownum <= 20
order by name )
where r > 10

�q�样取出�W?1-20条记�?(先选再排序再�?

要先排序再选则��ȝ��select嵌套�Q�内层排序外层选�?

rownum是随着�l�果集生成的�Q�一旦生成，��׃��?x��)变化�?ji��n)�Q�同�?生成的结果是依次递加的，没有1��永�q�不�?x��)�?!

rownum 是在查询集合产生的过�E�中产生的伪列，�q�且如果where条�g中存�?rownum 条�g的话�Q�则:

1�Q?假如判定条�g是常量，则：(x��)

只能 rownum = 1, <= 大于1 的自然数�Q?= 大于1 的数是没有结果的�Q?大于一个数也是没有�l�果�?

�?当出��C��?rownum 不满��x(ch��ng)��件的时候则查询�l�束　　this is stop key!

2: 当判定��g��是常量的时�?

若条件是 = var , 则只有当 var �? 的时候才满��条�g�Q�这个时候不存在 stop key ,必须�q�行 full scan ,�Ҏ(gu��)��个满��_��他where条�g的数据进行判�?

选出一行后才能去选rownum=2的行…�?

11�Q�快速编译所有视�?/STRONG>

---- 当在把数据库倒入到新的服务器上后(数据库重�?�Q�需要将视图重新�~�译一遍，因�ؓ(f��)该表�I�间视图到其它表�I�间的表的连接会(x��)出现问题�Q�可以利用PL/SQL的语�a��Ҏ(gu��)��，快速编译�?

SQL >SPOOL ON.SQL
SQL >SELECT ‘ALTER VIEW ‘||TNAME||�?
COMPILE;�?FROM TAB;
SQL >SPOOL OFF

然后执行ON.SQL卛_��?

SQL >@ON.SQL

当然�Q�授权和创徏同义词也可以快速进行，如：(x��)

SQL >SELECT ‘GRANT SELECT ON �?BR>||TNAME||�?TO USERNAME;�?FROM TAB;
SQL >SELECT ‘CREATE SYNONYM
‘||TNAME||�?FOR USERNAME.’||TNAME||�?�?FROM TAB;

12�Q�读写文本型操作�pȝ��文�g

---- 在PL/SQL 3.3以上的版本中�Q�UTL_FILE包允许用户通过PL/SQL��d��操作�pȝ��文�g。如下：(x��)

DECALRE
FILE_HANDLE UTL_FILE.FILE_TYPE;
BEGIN
FILE_HANDLE:=UTL_FILE.FOPEN(
‘C:\�?’TEST.TXT�?’A�?;
UTL_FILE.PUT_LINE(FILE_HANDLE,�?BR>HELLO,IT’S A TEST TXT FILE�?;
UTL_FILE.FCLOSE(FILE_HANDLE);
END;

13�Q�在数据库触发器中��用列的新��g��旧�?/STRONG>

---- 在数据库触发器中几乎��L��要��用触发器��的列��|��如果某条语句需要某列修改前的��|��使用:OLD��可以了(ji��n)�Q��用某列修改后的新��|��?NEW��可以了(ji��n)。如:OLD.DEPT_NO,:NEW.DEPT_NO�?

14�Q�数据库文�g的移动方�?/STRONG>

当想��数据库文�g�U�d��到另外一个目录下�Ӟ��可以用ALTER DATABASE命��o(h��)来移�?比ALTER TABLESPACE适用性强)�Q?

1. 使用SERVER MANAGER关闭实例.

SVRMGR > connect internal;
SVRMGR > shutdown;
SVRMGR >exit;

2. 使用操作�pȝ��命��o(h��)来移动数据库文�g位置(假设�q�里操作�pȝ��为SOLARIS 2.6). 在UNIX中用 mv命��o(h��)可以把文件移动到新的位置�Q?

#mv /ora13/orarun/document.dbf /ora12/orarun

3. 装蝲数据库�ƈ用alter database命��o(h��)来改变数据库中的文�g�?

SVRMGR > connect internal;
SVRMGR > startup mount RUN73;
SVRMGR > alter database rename file
> �? ora13/orarun/document.dbf�?
> �? ora12/orarun/document.dbf�?

4. 启动实例.

SVRMGR > alter database open;

15�Q�连接查询结果：(x��)

表a �?a1 a2

记录 1 a

1 b

2 x

2 y

2 z

用select能选成以下�l�果:

1 ab

2 xyz

下面有两个例子：(x��)

1.使用pl/sql代码实现�Q�但要求你组合后的长度不能超出oracle varchar2长度的限�?

create or replace type strings_table is table of varchar2(20);
/
create or replace function merge (pv in strings_table) return varchar2
is
ls varchar2(4000);
begin
for i in 1..pv.count loop
ls := ls || pv(i);
end loop;
return ls;
end;
/
create table t (id number,name varchar2(10));
insert into t values(1,'Joan');
insert into t values(1,'Jack');
insert into t values(1,'Tom');
insert into t values(2,'Rose');
insert into t values(2,'Jenny');
column names format a80;
select t0.id,merge(cast(multiset(select name from t where t.id = t0.id) as strings_table)) names
from (select distinct id from t) t0;
drop type strings_table;
drop function merge;
drop table t;

2.�U��a(b��)用sql�Q?

表dept, emp

要得到如下结�?

deptno, dname, employees

---------------------------------

10, accounting, clark;king;miller
20, research, smith;adams;ford;scott;jones
30, sales, allen;blake;martin;james;turners

每个dept的employee串�v来作��Z��条记录返�?

This example uses a max of 6, and would need more cut n pasting to do more than that�Q?
SQL> select deptno, dname, emps
2 from (
3 select d.deptno, d.dname, rtrim(e.ename ||', '||
4 lead(e.ename,1) over (partition by d.deptno
5 order by e.ename) ||', '||
6 lead(e.ename,2) over (partition by d.deptno
7 order by e.ename) ||', '||
8 lead(e.ename,3) over (partition by d.deptno
9 order by e.ename) ||', '||
10 lead(e.ename,4) over (partition by d.deptno
11 order by e.ename) ||', '||
12 lead(e.ename,5) over (partition by d.deptno
13 order by e.ename),', ') emps,
14 row_number () over (partition by d.deptno
15 order by e.ename) x
16 from emp e, dept d
17 where d.deptno = e.deptno
18 )
19 where x = 1
20 /

DEPTNO DNAME EMPS

------- ----------- ------------------------------------------

10 ACCOUNTING CLARK, KING, MILLER

20 RESEARCH ADAMS, FORD, JONES, ROONEY, SCOTT, SMITH

30 SALES ALLEN, BLAKE, JAMES, MARTIN, TURNER, WARD

16�Q�在Oracle中徏一个编号会(x��)自动增加的字�D?以利于查�?/STRONG>

1、徏立序列：(x��)

CREATE SEQUENCE checkup_no_seq
NOCYCLE
MAXVALUE 9999999999
START WITH 2;

2、徏立触发器�Q?

CREATE OR REPLACE TRIGGER set_checkup_no
BEFORE INSERT ON checkup_history
FOR EACH ROW
DECLARE
next_checkup_no NUMBER;
BEGIN
--Get the next checkup number from the sequence
SELECT checkup_no_seq.NEXTVAL
INTO next_checkup_no
FROM dual;

--use the sequence number as the primary key
--for the record being inserted
:new.checkup_no := next_checkup_no;
END;

17�Q�查看对象的依赖关系(比如视图与表的引�?

查看视图�Q�dba_dependencies 记录�?ji��n)相关的依赖关�?

查东西不知道要查看哪个视图时�Q�可以在DBA_Objects里看�Q?

select object_name from dba_objects where object_name like '%ROLE%'(假如查看ROLE相关)

然后DESC一下就大体上知道了(ji��n)�?/FONT>

18�Q�要扑ֈ�某月中所有周五的具体日期

select to_char(t.d,'YY-MM-DD') from (
select trunc(sysdate, 'MM')+rownum-1 as d
from dba_objects
where rownum < 32) t
where to_char(t.d, 'MM') = to_char(sysdate, 'MM') --扑և�当前月䆾的周五的日期
and trim(to_char(t.d, 'Day')) = '星期�?

--------

03-05-02

03-05-09

03-05-16

03-05-23

03-05-30

如果把where to_char(t.d, 'MM') = to_char(sysdate, 'MM')�Ҏ(gu��)��sysdate-90�Q�即为查扑ֽ�前月份的前三个月中的每周五的日期�?/FONT>

Stephen 2005-12-21 11:02 发表评论

Stephen — Fri, 09 Dec 2005 03:31:00 GMT
表user_test �l�构:
user_id| user_cname | user_age| others.....
name有重复项,Id��Z��?age为number,others为其他很多字�D?BR>求一查询
1)Name不能重复,
2)如果Name有重复去�q�龄最大的一条数�?BR>3)要求能查�?包括ID和others其他字段

在csdn上的�|�友帮我完成�?ji��n)一�U�答�?
select * from user_test where user_id in(
select max(user_id) from(
select a.user_id, a.user_cname , a.user_age from user_test a ,
(select user_cname, max(user_age) as maxage from user_test group by user_cname ) b
where a.user_cname = b.user_cname and a.user_age = b.maxage)
group by user_cname)

�q�种�{�案能满��?但是好像嵌套�q�多,呵呵,也许�?x��)�?ji��ng)响效�?BR>
我在itpub�?一位网友给�?ji��n)另一�U�答�?
select * from (select user_id, user_cname, user_age,
row_number() over(
partition by user_cname order by user_age desc
) rn
from user_test)
where rn =1

so cool ,isn't it?

Stephen 2005-12-09 11:31 发表评论

字符大对象Blob

Stephen — Sat, 19 Nov 2005 16:19:00 GMT
     摘要:                                  &n...  阅读全文

Stephen 2005-11-20 00:19 发表评论

Oracle里时间的应用

Stephen — Mon, 25 Apr 2005 05:47:00 GMT
1、�{换函�?BR>与date操作关系最大的��是两个转换函数�Q�to_date(),to_char()
to_date() 作用��字�W�类型按一定格式�{化�ؓ(f��)日期�c�d��Q?BR>具体用法:to_date('2004-11-27','yyyy-mm-dd'),前者�ؓ(f��)字符�Ԍ��后者�ؓ(f��)转换日期格式�Q�注意，前后两者要以一对应�?BR>�?to_date('2004-11-27 13:34:43', 'yyyy-mm-dd hh24:mi:ss') ��得到具体的旉��

多种日期格式�Q?BR>
YYYY�Q�四位表�C�的�q�䆾
YYY�Q�YY�Q�Y�Q�年份的最后三位、两位或一位，�~�省为当前世�U?
MM�Q?1~12的月份编�?
MONTH�Q�九(ji��)个字�W�表�C�的月䆾�Q�右边用�I�格填补
MON�Q�三位字�W�的月䆾�~�写
WW�Q�一�q�中的星�?
D�Q�星期中的第几天
DD�Q�月份中的第几天
DDD�Q�年所中的�W�几�?
DAY�Q�九(ji��)个字�W�表�C�的天的全称�Q�右边用�I�格补齐
HH�Q�HH12�Q�一天中的第几个��时�Q?2�q�制表示�?
HH24�Q�一天中的第几个��时�Q�取��gؓ(f��)00~23
MI�Q�一��时中的分钟
SS�Q�一分钟中的�U?
SSSS�Q�从午夜开始过�ȝ��U�数

to_char():��日期�{按一定格式换成字�W�类�?BR>SQL> select to_char(sysdate,'yyyy-mm-dd hh24:mi:ss') time from dual;

TIME
-------------------
2004-10-08 15:22:58

��x(ch��ng)��当前旉��按yyyy-mm-dd hh24:mi:ss格式转换成字�W�类�?BR>
在oracle中处理日期大�?

  TO_DATE格式
Day:
dd number 12
dy abbreviated fri
day spelled out friday
ddspth spelled out, ordinal twelfth
Month:
mm number 03
mon abbreviated mar
month spelled out march
Year:
yy two digits 98
yyyy four digits 1998

24��时格式下时间范围�ؓ(f��)�Q?0:00:00 - 23:59:59....
12��时格式下时间范围�ؓ(f��)�Q?1:00:00 - 12:59:59 ....

[ZT]日期和時間函數匯�^?/FONT>
1.
日期和字�W��{换函数用法（to_date,to_char�Q?nbsp;

2.
select to_char( to_date(222,'J'),'Jsp') from dual

昄��Two Hundred Twenty-Two

3.
求某天是星期�?nbsp;
select to_char(to_date('2002-08-26','yyyy-mm-dd'),'day') from dual;
星期一
select to_char(to_date('2002-08-26','yyyy-mm-dd'),'day','NLS_DATE_LANGUAGE = American') from dual;
monday
讄��日期语言
ALTER SESSION SET NLS_DATE_LANGUAGE='AMERICAN';
也可以这�?nbsp;
TO_DATE ('2002-08-26', 'YYYY-mm-dd', 'NLS_DATE_LANGUAGE = American')

4.
两个日期间的天数
select floor(sysdate - to_date('20020405','yyyymmdd')) from dual;

5. 旉��为null的用�?nbsp;
select id, active_date from table1
UNION
select 1, TO_DATE(null) from dual;

注意要用TO_DATE(null)

6.
a_date between to_date('20011201','yyyymmdd') and to_date('20011231','yyyymmdd')
那么12�?1号中�?2点之后和12�?��L(f��ng)��12点之前是不包含在�q�个范围之内的�?nbsp;
所以，当时间需要精��的时候，觉得to_char�q�是必要�?nbsp;
7. 日期格式冲突问题
输入的格式要看你安装的ORACLE字符集的�c�d��, 比如: US7ASCII, date格式的类型就�? '01-Jan-01'
alter system set NLS_DATE_LANGUAGE = American
alter session set NLS_DATE_LANGUAGE = American
或者在to_date中写
select to_char(to_date('2002-08-26','yyyy-mm-dd'),'day','NLS_DATE_LANGUAGE = American') from dual;
注意我这只是举了(ji��n)NLS_DATE_LANGUAGE�Q�当然还有很多，
可查�?nbsp;
select * from nls_session_parameters
select * from V$NLS_PARAMETERS

8.
select count(*)
from ( select rownum-1 rnum
from all_objects
where rownum <= to_date('2002-02-28','yyyy-mm-dd') - to_date('2002-
02-01','yyyy-mm-dd')+1
)
where to_char( to_date('2002-02-01','yyyy-mm-dd')+rnum-1, 'D' )
not
in ( '1', '7' )

查找2002-02-28�?002-02-01间除星期一和七的天�?nbsp;
在前后分别调用DBMS_UTILITY.GET_TIME, 让后��结果相�?得到的是1/100�U? 而不是毫�U?.

9.
select months_between(to_date('01-31-1999','MM-DD-YYYY'),
to_date('12-31-1998','MM-DD-YYYY')) "MONTHS" FROM DUAL;
1

select months_between(to_date('02-01-1999','MM-DD-YYYY'),
to_date('12-31-1998','MM-DD-YYYY')) "MONTHS" FROM DUAL;

1.03225806451613
10. Next_day的用�?nbsp;
Next_day(date, day)

Monday-Sunday, for format code DAY
Mon-Sun, for format code DY
1-7, for format code D

11
select to_char(sysdate,'hh:mi:ss') TIME from all_objects
注意�Q�第一条记录的TIME 与最后一行是一��L(f��ng)��
可以建立一个函数来处理�q�个问题
create or replace function sys_date return date is
begin
return sysdate;
end;

select to_char(sys_date,'hh:mi:ss') from all_objects;
12.
获得��时�?nbsp;

SELECT EXTRACT(HOUR FROM TIMESTAMP '2001-02-16 2:38:40') from offer
SQL> select sysdate ,to_char(sysdate,'hh') from dual;

SYSDATE TO_CHAR(SYSDATE,'HH')
-------------------- ---------------------
2003-10-13 19:35:21 07

SQL> select sysdate ,to_char(sysdate,'hh24') from dual;

SYSDATE TO_CHAR(SYSDATE,'HH24')
-------------------- -----------------------
2003-10-13 19:35:21 19

获取�q�月日与此类�?nbsp;
13.
�q�月日的处理
select older_date,
newer_date,
years,
months,
abs(
trunc(
newer_date-
add_months( older_date,years*12+months )
)
) days
from ( select
trunc(months_between( newer_date, older_date )/12) YEARS,
mod(trunc(months_between( newer_date, older_date )),
12 ) MONTHS,
newer_date,
older_date
from ( select hiredate older_date,
add_months(hiredate,rownum)+rownum newer_date
from emp )
)

14.
处理月䆾天数不定的办�?nbsp;
select to_char(add_months(last_day(sysdate) +1, -2), 'yyyymmdd'),last_day(sysdate) from dual

16.
扑և�今年的天�?nbsp;
select add_months(trunc(sysdate,'year'), 12) - trunc(sysdate,'year') from dual

闰年的处理方�?nbsp;
to_char( last_day( to_date('02' || :year,'mmyyyy') ), 'dd' )
如果�?8��׃��是闰�q?nbsp;

17.
yyyy与rrrr的区�?nbsp;
'YYYY99 TO_C
------- ----
yyyy 99 0099
rrrr 99 1999
yyyy 01 0001
rrrr 01 2001

18.不同时区的处�?nbsp;
select to_char( NEW_TIME( sysdate, 'GMT','EST'), 'dd/mm/yyyy hh:mi:ss') ,sysdate
from dual;

19.
5�U�钟一个间�?nbsp;
Select TO_DATE(FLOOR(TO_CHAR(sysdate,'SSSSS')/300) * 300,'SSSSS') ,TO_CHAR(sysdate,'SSSSS')
from dual

2002-11-1 9:55:00 35786
SSSSS表示5位秒�?nbsp;

20.
一�q�的�W�几�?nbsp;
select TO_CHAR(SYSDATE,'DDD'),sysdate from dual
310 2002-11-6 10:03:51

21.计算��时,�?�U?毫秒
select
Days,
A,
TRUNC(A*24) Hours,
TRUNC(A*24*60 - 60*TRUNC(A*24)) Minutes,
TRUNC(A*24*60*60 - 60*TRUNC(A*24*60)) Seconds,
TRUNC(A*24*60*60*100 - 100*TRUNC(A*24*60*60)) mSeconds
from
(
select
trunc(sysdate) Days,
sysdate - trunc(sysdate) A
from dual
)

select * from tabname
order by decode(mode,'FIFO',1,-1)*to_char(rq,'yyyymmddhh24miss');

//
floor((date2-date1) /365) 作�ؓ(f��)�q?nbsp;
floor((date2-date1, 365) /30) 作�ؓ(f��)�?nbsp;
mod(mod(date2-date1, 365), 30)作�ؓ(f��)�?
23.next_day函数
next_day(sysdate,6)是从当前开始下一个星期五。后面的数字是从星期日开始算赗��?nbsp;
1 2 3 4 5 6 7
�?一 �?�?�?�?�?BR>
oracle中有很多关于日期的函�?BR>
在oracle中有很多关于日期的函敎ͼ�如：(x��)
1、add_months()用于从一个日期值增加或减少一些月�?
date_value:=add_months(date_value,number_of_months)
例：(x��)
SQL> select add_months(sysdate,12) "Next Year" from dual;

Next Year
----------
13-11�?04

SQL> select add_months(sysdate,112) "Last Year" from dual;

Last Year
----------
13-3�?-13

SQL>

2、current_date()�q�回当前�?x��)放时区中的当前日�?
date_value:=current_date
SQL> column sessiontimezone for a15
SQL> select sessiontimezone,current_date from dual;

SESSIONTIMEZONE CURRENT_DA
--------------- ----------
+08:00 13-11�?03

SQL> alter session set time_zone='-11:00'
  2 /

�?x��)话已更攏V�?

SQL> select sessiontimezone,current_timestamp from dual;

SESSIONTIMEZONE CURRENT_TIMESTAMP
--------------- ------------------------------------
-11:00 12-11�?03 04.59.13.668000 下午 -11:
            00

SQL>

3、current_timestamp()以timestamp with time zone数据�c�d��q�回当前�?x��)放时区中的当前日�?
timestamp_with_time_zone_value:=current_timestamp([timestamp_precision])
SQL> column sessiontimezone for a15
SQL> column current_timestamp format a36
SQL> select sessiontimezone,current_timestamp from dual;

SESSIONTIMEZONE CURRENT_TIMESTAMP
--------------- ------------------------------------
+08:00 13-11�?03 11.56.28.160000 上午 +08:
            00

SQL> alter session set time_zone='-11:00'
  2 /

�?x��)话已更攏V�?

SQL> select sessiontimezone,current_timestamp from dual;

SESSIONTIMEZONE CURRENT_TIMESTAMP
--------------- ------------------------------------
-11:00 12-11�?03 04.58.00.243000 下午 -11:
            00

SQL>

4、dbtimezone()�q�回时区
varchar_value:=dbtimezone
SQL> select dbtimezone from dual;

DBTIME
------
-07:00

SQL>

5、extract()扑և�日期或间隔值的字段�?
date_value:=extract(date_field from [datetime_value|interval_value])
SQL> select extract(month from sysdate) "This Month" from dual;

This Month
----------
      11

SQL> select extract(year from add_months(sysdate,36)) "3 Years Out" from dual;

3 Years Out
-----------
   2006

SQL>

6、last_day()�q�回包含�?ji��n)日期参数的月䆾的最后一天的日期
date_value:=last_day(date_value)
SQL> select last_day(date'2000-02-01') "Leap Yr?" from dual;

Leap Yr?
----------
29-2�?-00

SQL> select last_day(sysdate) "Last day of this month" from dual;

Last day o
----------
30-11�?03

SQL>

7、localtimestamp()�q�回�?x��)话中的日期和时�?
timestamp_value:=localtimestamp
SQL> column localtimestamp format a28
SQL> select localtimestamp from dual;

LOCALTIMESTAMP
----------------------------
13-11�?03 12.09.15.433000
下午

SQL> select localtimestamp,current_timestamp from dual;

LOCALTIMESTAMP CURRENT_TIMESTAMP
---------------------------- ------------------------------------
13-11�?03 12.09.31.006000 13-11�?03 12.09.31.006000 下午 +08:
下午 00

SQL> alter session set time_zone='-11:00';

�?x��)话已更攏V�?

SQL> select localtimestamp,to_char(sysdate,'DD-MM-YYYY HH:MI:SS AM') "SYSDATE" from dual;

LOCALTIMESTAMP SYSDATE
---------------------------- ------------------------
12-11�?03 05.11.31.259000 13-11-2003 12:11:31 下午
下午

SQL>

8、months_between()判断两个日期之间的月份数�?
number_value:=months_between(date_value,date_value)
SQL> select months_between(sysdate,date'1971-05-18') from dual;

MONTHS_BETWEEN(SYSDATE,DATE'1971-05-18')
----------------------------------------
                           389.855143

SQL> select months_between(sysdate,date'2001-01-01') from dual;

MONTHS_BETWEEN(SYSDATE,DATE'2001-01-01')
----------------------------------------
                           34.4035409

SQL>

9、next_day()�l�定一个日期��|��q�回��q��二个参数指出的日子第一�ơ出现在的日期��|��应返回相应日子的名称字符�Ԍ��(j��)

與周盔R��日期函數

1.查询某周的第一�?BR>select trunc(decode(ww, 53, to_date(yy || '3112', 'yyyyddmm'), to_date(yy || '-' || to_char(ww * 7), 'yyyy-ddd')), 'd') last_day
from (select substr('2004-32', 1, 4) yy, to_number(substr('2004-32', 6)) ww
      from dual)

select trunc(to_date(substr('2003-01',1,5)||to_char((to_number(substr('2003-01',6)))*7),'yyyy-ddd'),'d')-6 first_day from dual

select min(v_date) from
  (select (to_date('200201','yyyymm') + rownum) v_date
  from all_tables
  where rownum < 370)
where to_char(v_date,'yyyy-iw') = '2002-49'

2.查询某周的最后一�?BR>select trunc(decode(ww, 53, to_date(yy || '3112', 'yyyyddmm'), to_date(yy || '-' || to_char(ww * 7), 'yyyy-ddd')), 'd') - 6 first_day
  from (select substr('2004-33', 1, 4) yy, to_number(substr('2004-33', 6)) ww
      from dual)

select trunc(to_date(substr('2003-01',1,5)||to_char((to_number(substr('2003-01',6)))*7),'yyyy-ddd'),'d') last_day from dual

select max(v_date) from
  (select (to_date('200408','yyyymm') + rownum) v_date
  from all_tables
  where rownum < 370)
where to_char(v_date,'yyyy-iw') = '2004-33'

3.查询某周的日�?BR>select min_date, to_char(min_date,'day') day from
(select to_date(substr('2004-33',1,4)||'001'+rownum-1,'yyyyddd') min_date
      from all_tables
  where rownum <= decode(mod(to_number(substr('2004-33',1,4)),4),0,366,365)
  union

  select to_date(substr('2004-33',1,4)-1||
      decode(mod(to_number(substr('2004-33',1,4))-1,4),0,359,358)+rownum,'yyyyddd') min_date
      from all_tables
      where rownum <= 7
  union

  select to_date(substr('2004-33',1,4)+1||'001'+rownum-1,'yyyyddd') min_date
      from all_tables
      where rownum <= 7
)
where to_char(min_date,'yyyy-iw') ='2004-33'

Stephen 2005-04-25 13:47 发表评论