ORACLE字符串处理函数(2)

ADD_MONTHS

增加或减去月份

SQL> select to_char(add_months(to_date(yyyymm))yyyymm) from dual;

TO_CHA

SQL> select to_char(add_months(to_date(yyyymm))yyyymm) from dual;

TO_CHA

LAST_DAY

返回日期的最后一天

SQL> select to_char(sysdateyyyymmdd)to_char((sysdate)+yyyymmdd) from dual;

TO_CHAR(SY TO_CHAR((S

SQL> select last_day(sysdate) from dual;

LAST_DAY(S

月

MONTHS_BETWEEN(datedate)

给出datedate的月份

SQL> select months_between(月月) mon_between from dual;

MON_BETWEEN

SQL>selectmonths_between(to_date(yyyymmdd)to_date(yyyymmdd)) mon_betw from dual;

MON_BETW

NEW_TIME(datethisthat)

给出在this时区=other时区的日期和时间

SQL> select to_char(sysdateyyyymmdd hh:mi:ss) bj_timeto_char(new_time

(sysdatePDTGMT)yyyymmdd hh:mi:ss) los_angles from dual;

BJ_TIME LOS_ANGLES

:: ::

NEXT_DAY(dateday)

给出日期date和星期x之后计算下一个星期的日期

SQL> select next_day(月星期五) next_day from dual;

NEXT_DAY

月

SYSDATE

用来得到系统的当前日期

SQL> select to_char(sysdateddmmyyyy day) from dual;

TO_CHAR(SYSDATE

星期日

trunc(datefmt)按照给出的要求将日期截断如果fmt=mi表示保留分截断秒

SQL> select to_char(trunc(sysdatehh)yyyymmdd hh:mi:ss) hh

to_char(trunc(sysdatemi)yyyymmdd hh:mi:ss) hhmm from dual;

HH HHMM

:: ::

CHARTOROWID

将字符数据类型转换为ROWID类型

SQL> select rowidrowidtochar(rowid)ename from scottemp;

ROWID ROWIDTOCHAR(ROWID) ENAME

AAAAfKAACAAAAEqAAA AAAAfKAACAAAAEqAAA SMITH

AAAAfKAACAAAAEqAAB AAAAfKAACAAAAEqAAB ALLEN

AAAAfKAACAAAAEqAAC AAAAfKAACAAAAEqAAC WARD

AAAAfKAACAAAAEqAAD AAAAfKAACAAAAEqAAD JONES

CONVERT(cdsetsset)

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(strutzwehpfdec) conversion from dual;

conver

strutz

HEXTORAW

将一个十六进制构成的字符串转换为二进制

RAWTOHEXT

将一个二进制构成的字符串转换为十六进制

ROWIDTOCHAR

将ROWID数据类型转换为字符类型

TO_CHAR(dateformat)

SQL> select to_char(sysdateyyyy/mm/dd hh:mi:ss) from dual;

TO_CHAR(SYSDATEYY

// ::

TO_DATE(stringformat)

将字符串转化为ORACLE中的一个日期

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

TO_NUMBER

将给出的字符转换为数字

SQL> select to_number() year from dual;

YEAR

BFILENAME(dirfile)

指定一个外部二进制文件

SQL>insert into file_tb values(bfilename(lob_dirimagegif));

CONVERT(xdescsource)

将x字段或变量的源source转换为desc

SQL> select sidserial#usernamedecode(command

none

insert

select

update

delete

drop

other) cmd from v$session where type!=background;

SID SERIAL# USERNAME CMD

none

none

none

none

none

none

none

none

GAO select

GAO none

DUMP(sfmtstartlength)

DUMP函数以fmt指定的内部数字格式返回一个VARCHAR类型的值

SQL> col global_name for a

SQL> col dump_string for a

SQL> set lin

SQL> select global_namedump(global_name) dump_string from global_name;

GLOBAL_NAME DUMP_STRING

ORACLEWORLD Typ= Len= CharacterSet=ZHSGBK: WORLD

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

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(AAABAC) from dual;

GR

AC

SQL> select greatest(啊安天) from dual;

GR

天

LEAST

返回一组表达式中的最小值

SQL> select least(啊安天) from dual;

LE

啊

UID

返回标识当前用户的唯一整数

SQL> show user

USER 为GAO

SQL> select usernameuser_id from dba_users where user_id=uid;

USERNAME USER_ID

GAO

USER

返回当前用户的名字

SQL> select user from dual;

USER

GAO

USEREVN

返回当前用户环境的信息opt可以是:

ENTRYIDSESSIONIDTERMINALISDBALABLELANGUAGECLIENT_INFOLANGVSIZE

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)

ENTRYID

返回会话人口标志

SQL> select userenv(entryid) from dual;

USERENV(ENTRYID)

INSTANCE

返回当前INSTANCE的标志

SQL> select userenv(instance) from dual;

USERENV(INSTANCE)

LANGUAGE

返回当前环境变量

SQL> select userenv(language) from dual;

USERENV(LANGUAGE)

SIMPLIFIED CHINESE_CHINAZHSGBK

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

SYSTEM

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 table(xm varchar()sal number());

语句已处理

SQLWKS> insert into table values(gao);

SQLWKS> insert into table values(gao);

SQLWKS> insert into table values(zhu);

SQLWKS> commit;

SQL> select avg(distinct sal) from gaotable;

AVG(DISTINCTSAL)

SQL> select avg(all sal) from gaotable;

AVG(ALLSAL)

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 scottemp;

MAX(DISTINCTSAL)

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 gaotable;

MIN(ALLSAL)

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 scottemp;

STDDEV(SAL)

SQL> select stddev(distinct sal) from scottemp;

STDDEV(DISTINCTSAL)

VARIANCE(DISTINCT|ALL)

求协方差

SQL> select variance(sal) from scottemp;

VARIANCE(SAL)

GROUP BY

主要用来对一组数进行统计

SQL> select deptnocount(*)sum(sal) from scottemp group by deptno;

DEPTNO COUNT(*) SUM(SAL)

HAVING

对分组统计再加限制条件

SQL> select deptnocount(*)sum(sal) from scottemp group by deptno having count(*)>=;

DEPTNO COUNT(*) SUM(SAL)

SQL> select deptnocount(*)sum(sal) from scottemp having count(*)>= group by deptno ;

DEPTNO COUNT(*) SUM(SAL)

ORDER BY

用于对查询到的结果进行排序输出

SQL> select deptnoenamesal from scottemp order by deptnosal desc;

DEPTNO ENAME SAL

KING

CLARK

MILLER

SCOTT

FORD

JONES

ADAMS

SMITH

BLAKE

ALLEN

TURNER

WARD

MARTIN

JAMES