Oracle SQL 内置函数大全(3)

43.CONVERT(c,dset,sset)
将源字符串 sset从一个语言字符集转换到另一个目的dset字符集
SQL> select convert('strutz','we8hp','f7dec') "conversion" from dual;

conver
------
strutz

44.HEXTORAW 将一个十六进制构成的字符串转换为二进制

45.RAWTOHEXT 将一个二进制构成的字符串转换为十六进制

46.ROWIDTOCHAR 将ROWID数据类型转换为字符类型

47.TO_CHAR(date,'format')
SQL> select to_char(sysdate,'yyyy/mm/dd hh24:mi:ss') from dual;

TO_CHAR(SYSDATE,'YY
-------------------
2004/05/09 21:14:41

48.TO_DATE(string,'format') 将字符串转化为ORACLE中的一个日期

49.TO_MULTI_BYTE  将字符串中的单字节字符转化为多字节字符
SQL>  select to_multi_byte('高') from dual;

TO
--
高

50.TO_NUMBER
将给出的字符转换为数字
SQL> select to_number('1999') year from dual;

YEAR
---------
1999

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
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