Oracle数据库常用函数(3)
发布时间：2010/7/26 10:46:53 来源：城市学习网 编辑：ziteng
51.BFILENAME(dir,file)
指定一个外部二进制文件
SQL>insert into file_tb1 values(bfilename(lob_dir1,image1.gif));
52.CONVERT(x,desc,source)
将x字段或变量的源source转换为desc
SQL> select sid,serial#,username,decode(command,
2 0,none,
3 2,insert,
4 3,
5 select,
6 6,update,
7 7,delete,
8 8,drop,
9 other) cmd from v$session where type!=background;
SID SERIAL# USERNAME CMD
--------- --------- ------------------------------ ------
1 1 none
2 1 none
3 1 none
4 1 none
5 1 none
6 1 none
7 1275 none
8 1275 none
9 20 GAO select
10 40 GAO none
53.DUMP(s,fmt,start,length)
DUMP函数以fmt指定的内部数字格式返回一个VARCHAR2类型的值
SQL> col global_name for a30
SQL> col dump_string for a50
SQL> set lin 200
SQL> select global_name,dump(global_name,1017,8,5) dump_string from global_name;
GLOBAL_NAME DUMP_STRING
------------------------------ --------------------------------------------------
ORACLE.WORLD Typ=1 Len=12 CharacterSet=ZHS16GBK: W,O,R,L,D
54.EMPTY_BLOB()和EMPTY_CLOB()
这两个函数都是用来对大数据类型字段进行初始化操作的函数
55.GREATEST
返回一组表达式中的最大值,即比较字符的编码大小.
SQL> select greatest(AA,AB,AC) from dual;
GR
--
AC
SQL> select greatest(啊,安,天) from dual;
GR
--
天
56.LEAST
返回一组表达式中的最小值
SQL> select least(啊,安,天) from dual;
LE
--
啊
57.UID
返回标识当前用户的唯一整数
SQL> show user
USER 为"GAO"
SQL> select username,user_id from dba_users where user_id=uid;
USERNAME USER_ID
------------------------------ ---------
GAO 25
58.USER
返回当前用户的名字
SQL> select user from dual;
USER
------------------------------
GAO
59.USEREVN
返回当前用户环境的信息,opt可以是:
ENTRYID,SESSIONID,TERMINAL,ISDBA,LABLE,LANGUAGE,CLIENT_INFO,LANG,VSIZE
ISDBA 查看当前用户是否是DBA如果是则返回true
SQL> select userenv(isdba) from dual;
USEREN
------
FALSE
SQL> select userenv(isdba) from dual;
USEREN
------
TRUE
SESSION
返回会话标志
SQL> select userenv(sessionid) from dual;
USERENV(SESSIONID)
--------------------
152
ENTRYID
返回会话人口标志
SQL> select userenv(entryid) from dual;
USERENV(ENTRYID)
------------------
0
INSTANCE
返回当前INSTANCE的标志
SQL> select userenv(instance) from dual;
USERENV(INSTANCE)
-------------------
1 [NextPage] LANGUAGE
返回当前环境变量
SQL> select userenv(language) from dual;
USERENV(LANGUAGE)
----------------------------------------------------
SIMPLIFIED CHINESE_CHINA.ZHS16GBK
LANG
返回当前环境的语言的缩写
SQL> select userenv(lang) from dual;
USERENV(LANG)
----------------------------------------------------
ZHS
TERMINAL
返回用户的终端或机器的标志
SQL> select userenv(terminal) from dual;
USERENV(TERMINA
----------------
GAO
VSIZE(X)
返回X的大小(字节)数
SQL> select vsize(user),user from dual;
VSIZE(USER) USER
----------- ------------------------------
6 SYSTEM
? 60.AVG(DISTINCT|ALL)
all表示对所有的值求平均值,distinct只对不同的值求平均值
SQLWKS> create table table3(xm varchar(8),sal number(7,2));
语句已处理。
SQLWKS> insert into table3 values(gao,1111.11);
SQLWKS> insert into table3 values(gao,1111.11);
SQLWKS> insert into table3 values(zhu,5555.55);
SQLWKS> commit;
SQL> select avg(distinct sal) from gao.table3;
AVG(DISTINCTSAL)
----------------
3333.33
SQL> select avg(all sal) from gao.table3;
AVG(ALLSAL)
-----------
2592.59
61.MAX(DISTINCT|ALL)
求最大值,ALL表示对所有的值求最大值,DISTINCT表示对不同的值求最大值,相同的只取一次
SQL> select max(distinct sal) from scott.emp;
MAX(DISTINCTSAL)
----------------
5000
62.MIN(DISTINCT|ALL)
求最小值,ALL表示对所有的值求最小值,DISTINCT表示对不同的值求最小值,相同的只取一次
SQL> select min(all sal) from gao.table3;
MIN(ALLSAL)
-----------
1111.11
63.STDDEV(distinct|all)
求标准差,ALL表示对所有的值求标准差,DISTINCT表示只对不同的值求标准差
SQL> select stddev(sal) from scott.emp;
STDDEV(SAL)
-----------
1182.5032
SQL> select stddev(distinct sal) from scott.emp;
STDDEV(DISTINCTSAL)
-------------------
1229.951
64.VARIANCE(DISTINCT|ALL)
求协方差
SQL> select variance(sal) from scott.emp;
VARIANCE(SAL)
-------------
1398313.9
65.GROUP BY
主要用来对一组数进行统计
SQL> select deptno,count(*),sum(sal) from scott.emp group by deptno;
DEPTNO COUNT(*) SUM(SAL)
--------- --------- ---------
10 3 8750
20 5 10875
30 6 9400
66.HAVING
对分组统计再加限制条件
SQL> select deptno,count(*),sum(sal) from scott.emp group by deptno having count(*)>=5;
DEPTNO COUNT(*) SUM(SAL)
--------- --------- ---------
20 5 10875
30 6 9400
SQL> select deptno,count(*),sum(sal) from scott.emp having count(*)>=5 group by deptno ;
DEPTNO COUNT(*) SUM(SAL)
--------- --------- ---------
20 5 10875
30 6 9400
67.ORDER BY
用于对查询到的结果进行排序输出
SQL> select deptno,ename,sal from scott.emp order by deptno,sal desc;
DEPTNO ENAME SAL
--------- ---------- ---------
10 KING 5000
10 CLARK 2450
10 MILLER 1300
20 SCOTT 3000
20 FORD 3000
20 JONES 2975
20 ADAMS 1100
20 SMITH 800
30 BLAKE 2850
30 ALLEN 1600
30 TURNER 1500
30 WARD 1250
30 MARTIN 1250
30 JAMES 950
