单行函数
为了方便使用oracle数据库，sqlplus提供了大量的函数。
单行函数只对表中的一行进行操作，并且对每一行的输出只产生一个输出结果。
可用在 select，where，order by子句里，而且单行函数可以嵌套使用。
这是其返回类型与大致功能对象
首先介绍一下 dual表
首先是字符函数：
大小写转换：LOWER UPPER INITCAP
字符处理：CONCAT SUBSTR LENGTH INSTR LPAD RPAD TRIM
----------------
将字符转换为小写：lower
大写：upper
将每个单词的头转化为大写，其余小写
SQL> select lower('SQL:Structural Query Language') from dual;
LOWER('SQL:STRUCTURALQUERYLAN
-----------------------------
sql:structural query language
SQL>
SQL> select upper('sql is used exclusively in rdbmses') from dual;
UPPER('SQLISUSEDEXCLUSIVELYINRDBMS
----------------------------------
SQL IS USED EXCLUSIVELY IN RDBMSES
SQL>
SQL> select upper("sql is used exclusively in rdbmses") from dual;
select upper("sql is used exclusively in rdbmses") from dual
*
第 1 行出现错误:
ORA-00972: 标识符过长
SQL> select upper("sql is used exclusively in rdbmses") from dual;
select upper("sql is used exclusively in rdbmses") from dual
*
第 1 行出现错误:
ORA-00972: 标识符过长
SQL> //不可用“”
select upper("sql is used exclusively in rdbmses") from dual
*
第 1 行出现错误:
ORA-00972: 标识符过长
SQL> select initcap('SQL is an ENGLISH LIKE language') from dual;
INITCAP('SQLISANENGLISHLIKELANG
-------------------------------
Sql Is An English Like Language
concat(列名|表达式,列名|表达式)
链接两个字符串
substr(列名|表达式，m,[n])
其中n可选，返回一个字符串，从第m个字符开始，其长度为n。
SQL> select initcap('SQL is an ENGLISH LIKE language') from dual;
INITCAP('SQLISANENGLISHLIKELANG
-------------------------------
Sql Is An English Like Language
SQL>
SQL>
SQL> select concat('good','boy') from dual;
CONCAT(
-------
goodboy
SQL> select substr('ok,let we go to the city',3) from dual;
SUBSTR('OK,LETWEGOTOTH
----------------------
,let we go to the city
SQL>length(列名|表达式)
返回长度。
instr(列名|表达式,'字符串',[m],[n])
返回所给字符串的数字位置，m表示从第m个字符开始搜索，n表示第几次出现字符。m,n默认都是1
SQL> select length('we are good')from dual;
LENGTH('WEAREGOOD')
-------------------
11
SQL> select length("we are good")from dual;
select length("we are good")from dual
*
第 1 行出现错误:
ORA-00904: "we are good": 标识符无效
SQL> select instr('i am good man iam niubi','i') from dual;
INSTR('IAMGOODMANIAMNIUBI','I')
-------------------------------
1
SQL> select instr('i am good man iam niubi','i',n=2) from dual;
select instr('i am good man iam niubi','i',n=2) from dual
*
第 1 行出现错误:
ORA-00907: 缺失右括号
SQL> select instr('i am good man iam niubi','i',1,2) from dual;
INSTR('IAMGOODMANIAMNIUBI','I',1,2)
-----------------------------------
15trim([leading|trailing|both]from 源字符串）
默认是 both
leading头
trailing尾
也就是在头或者尾去掉一些东西
replace(正文表达式，要搜寻的字符串，用这个替换）
找到就替换
SQL> l
1 select trim('?' from '?sql*plus is the sql implementation
2 used in an oracle rdbms or ordbms.')
3* from dual
SQL> /
TRIM('?'FROM'?SQL*PLUSISTHESQLIMPLEMENTATIONUSEDINANORACLERDBMSORORDB
---------------------------------------------------------------------
sql*plus is the sql implementation
used in an oracle rdbms or ordbms.
SQL> select trim(trailing '?' from '?ok?') from dual;
TRI
---
?ok
SQL> select replace('ok i will go','wi','fuck') from dual;
REPLACE('OKIWI
--------------
ok i fuckll go
小小的应用一下：
SQL> select empno,ename ,job
2 from emp
3 where JOB='salesman';
未选定行
SQL>
SQL> 3
3* where JOB='salesman'
SQL> 3 where lower(job)='salesman'
SQL> l
1 select empno,ename ,job
2 from emp
3* where lower(job)='salesman'
SQL> /
EMPNO ENAME JOB
---------- ---------- ---------
7499 ALLEN SALESMAN
7521 WARD SALESMAN
7654 MARTIN SALESMAN
7844 TURNER SALESMAN
SQL> 3
3* where lower(job)='salesman'
SQL> 3 where lower('job')='salesman'
SQL> l
1 select empno,ename ,job
2 from emp
3* where lower('job')='salesman'
SQL> /
未选定行//因为是个列，所以不加‘’
=============
数字型函数：
SQL> select round(168.888,1),trunc(168.888,1) from dual;
ROUND(168.888,1) TRUNC(168.888,1)
---------------- ----------------
168.9 168.8
round(x,0)接收一个浮点数，0，1，2，3指多少位小数点 -1，-2，-3.。。。是个位，十位，百位等
trunc（，）是截取
SQL> select round(168.333,2),trunc(168.333,2) from dual;
ROUND(168.333,2) TRUNC(168.333,2)
---------------- ----------------
168.33 168.33
SQL> #
SQL> select round(168.888,0),trunc(168.888,0) from dual;
ROUND(168.888,0) TRUNC(168.888,0)
---------------- ----------------
169 168
SQL> select round(168.888),trunc(168.888) from fual;
select round(168.888),trunc(168.888) from fual
*
第 1 行出现错误:
ORA-00942: 表或视图不存在
SQL> select round(168.888),trunc(168.888) from dual;
ROUND(168.888) TRUNC(168.888)
-------------- --------------
169 168
SQL> select round(168.888,-1),trunc(168.888,-1) from dual;
ROUND(168.888,-1) TRUNC(168.888,-1)
----------------- -----------------
170 160
SQL> select mod(1900,400) from dual;
MOD(1900,400)
-------------
300
SQL> select mod(2000,400) from dual
2 ;
MOD(2000,400)
-------------
0
SQL> select mod(300,400) from dual;
MOD(300,400)
------------
300
-----------------------
日期函数：
日期型数据的处理：
Oracle数据库内的日期存储格式为： 世纪，年，月，日，时，分，秒从9i开始，日期型数据的输出和和输入默认是 DD-MON-RR
首先，将数据库日期型设置为美国英语：
>alter session set NLS_DATE_LANGUAGE='AMERICAN'
SQL> ALTER SESSION SET NLS_DATE_LANGUAGE='AMERICAN'
2 ;
会话已更改。
SQL> SELECT SYSDATE FROM DUAL;
SYSDATE
------------
01-APR-18
日期型与数字相加减，
两个日期型相减，不允许相加
一个小时数 23/24
SQL> SELECT SYSDATE FROM DUAL;
SYSDATE
------------
01-APR-18
SQL> select sysdate-10 from dual;
SYSDATE-10
------------
22-MAR-18
SQL> select sysdate+10 from dual;
SYSDATE+10
------------
11-APR-18
SQL> select to_date()
2 select to_date()
3 ;
select to_date()
*
第 2 行出现错误:
ORA-00923: 未找到要求的 FROM 关键字
SQL> select to_date('12-2-18')+sysdate from dual;
select to_date('12-2-18')+sysdate from dual
*
第 1 行出现错误:
ORA-00975: 不允许日期 + 日期
SQL> select to_date('12-2-18')-sysdate from dual;
select to_date('12-2-18')-sysdate from dual
*
第 1 行出现错误:
ORA-01843: 无效的月份
SQL> select to_date('12-JUL-18')-sysdate from dual;
TO_DATE('12-JUL-18')-SYSDATE
----------------------------
101.359144
SQL> select to_date('12-JUL-18')+sysdate from dual;
select to_date('12-JUL-18')+sysdate from dual
*
第 1 行出现错误:
ORA-00975: 不允许日期 + 日期
SQL> select sysdate-22/24 from dual;
SYSDATE-22/2
------------
31-MAR-18
SQL> select sysdate+22/24 from dual;
SYSDATE+22/2
------------
02-APR-18
SQL> select empno,ename,job,sal,(sysdate-hiredate)/365 as "Year"
2 from dual;
select empno,ename,job,sal,(sysdate-hiredate)/365 as "Year"
*
第 1 行出现错误:
ORA-00904: "HIREDATE": 标识符无效
SQL> select empno,ename,job,sal,(sysdate-hiredate)/365 as "Year"
2 from emp
3 where job LIKE 'SAL%';
EMPNO ENAME JOB SAL Year
---------- ---------- --------- ---------- ----------
7499 ALLEN SALESMAN 1600 37.136009
7521 WARD SALESMAN 1250 37.1305296
7654 MARTIN SALESMAN 1250 36.5332693
7844 TURNER SALESMAN 1500 36.5880638
SQL> #工龄
SP2-0042: 未知命令 "工龄" - 其余行忽略。
SQL>months_between(日期1，日期2）
1-2 的月数
add_months(日期，n）
日期加上n个月
next_day(日期，字符串）
字符串里是星期几
last_day(日期）
返回该日期所在月的最后一天
SQL> select months_between('01-JUL-12','03-FEB-11') from dual;
MONTHS_BETWEEN('01-JUL-12','03-FEB-11')
---------------------------------------
16.9354839
SQL> select add_months('15-OCT-11',8) from dual;
ADD_MONTHS('
------------
15-JUN-12
SQL> select next_date(sysdate,'MONDAY'） from dual;
select next_date(sysdate,'MONDAY'） from dual
*
第 1 行出现错误:
ORA-00904: "NEXT_DATE": 标识符无效
SQL> select next_day(sysdate,'MONDAY'） from dual;
NEXT_DAY(SYS
------------
02-APR-18
SQL> select last_day(sysdate) from dual;
LAST_DAY(SYS
------------
30-APR-18
SQL>
SQL> select ename,hiredate,LAST_DAY(hiredate),NEXT_DAY(hiredate,'
2 SUNDAY'),
3 MONTHS_BETWEEN(SYSDATE,hiredate) "Months",
4 ADD_MONTHS(hiredate,3) "Review"
5 FROM emp;
select ename,hiredate,LAST_DAY(hiredate),NEXT_DAY(hiredate,'
*
第 1 行出现错误:
ORA-01846: 周中的日无效
SQL> l
1 select ename,hiredate,LAST_DAY(hiredate),NEXT_DAY(hiredate,'
2 SUNDAY'),
3 MONTHS_BETWEEN(SYSDATE,hiredate) "Months",
4 ADD_MONTHS(hiredate,3) "Review"
5* FROM emp
SQL> 1 Change /'
SQL> l
1 Change /'
2 SUNDAY'),
3 MONTHS_BETWEEN(SYSDATE,hiredate) "Months",
4 ADD_MONTHS(hiredate,3) "Review"
5* FROM emp
SQL> select hiredate from emp;
HIREDATE
------------
17-DEC-80
20-FEB-81
22-FEB-81
02-APR-81
28-SEP-81
01-MAY-81
09-JUN-81
19-APR-87
17-NOV-81
08-SEP-81
23-MAY-87
HIREDATE
------------
03-DEC-81
03-DEC-81
23-JAN-82
已选择14行。
SQL> select ename,hiredate,LAST_DAY(hiredate),
2 next_day(hiredate,'SUNDAY'),
3 months_between(sysdate,hiredate)"months",
4 add_months(hiredate,3) "review"
5 from emp;
ENAME HIREDATE LAST_DAY(HIR NEXT_DAY(HIR months review
---------- ------------ ------------ ------------ ---------- ------------
SMITH 17-DEC-80 31-DEC-80 21-DEC-80 447.504965 17-MAR-81
ALLEN 20-FEB-81 28-FEB-81 22-FEB-81 445.40819 20-MAY-81
WARD 22-FEB-81 28-FEB-81 01-MAR-81 445.343674 22-MAY-81
JONES 02-APR-81 30-APR-81 05-APR-81 443.988835 02-JUL-81
MARTIN 28-SEP-81 30-SEP-81 04-OCT-81 438.150126 28-DEC-81
BLAKE 01-MAY-81 31-MAY-81 03-MAY-81 443 01-AUG-81
CLARK 09-JUN-81 30-JUN-81 14-JUN-81 441.763029 09-SEP-81
SCOTT 19-APR-87 30-APR-87 26-APR-87 371.440448 19-JUL-87
KING 17-NOV-81 30-NOV-81 22-NOV-81 436.504965 17-FEB-82
TURNER 08-SEP-81 30-SEP-81 13-SEP-81 438.795287 08-DEC-81
ADAMS 23-MAY-87 31-MAY-87 24-MAY-87 370.311416 23-AUG-87
ENAME HIREDATE LAST_DAY(HIR NEXT_DAY(HIR months review
---------- ------------ ------------ ------------ ---------- ------------
JAMES 03-DEC-81 31-DEC-81 06-DEC-81 435.956577 03-MAR-82
FORD 03-DEC-81 31-DEC-81 06-DEC-81 435.956577 03-MAR-82
MILLER 23-JAN-82 31-JAN-82 24-JAN-82 434.311416 23-APR-82
已选择14行。
SQL>
round 和trunc 用于日期型数据
round('20-OTC-11','MONTH') 这样是错的，没有自动转换，当作了字符串了，而round是不能处理字符串的。
反正round与trunc的区别是有无进位：
SQL> select round('28-OCT-11','MONTH') FROM dual;
select round('28-OCT-11','MONTH') FROM dual
*
第 1 行出现错误:
ORA-01722: 无效数字
SQL> select round(to_date('28-OCT-11'),'MONTH') FROM dual;
ROUND(TO_DAT
------------
01-NOV-11
SQL> select round(to_date('28-OCT-11'),'YEAR') FROM dual;
ROUND(TO_DAT
------------
01-JAN-12
SQL> select TRUNC(to_date('28-OCT-11'),'MONTH') FROM dual;
TRUNC(TO_DAT
------------
01-OCT-11
SQL> select TRUNC(to_date('28-OCT-11'),'YEAR') FROM dual;
TRUNC(TO_DAT
------------
01-JAN-11----------------
数据类型的转换，不管怎么说，大致分三类，数字，字符，日期
数字，与日期不可直接转换，必须通过字符这个桥梁来达到目的。
隐式转换我们就不说了 详见 单行函数 图
共有三个转换函数：
to_char(date,'fmt')
将日期转换为字符串格式。
SQL> select ename,to_char(hiredate,'DD/MM/YY') FROM dual;
select ename,to_char(hiredate,'DD/MM/YY') FROM dual
*
第 1 行出现错误:
ORA-00904: "HIREDATE": 标识符无效
SQL> select ename,to_char(hiredate,'DD/MM/YY') FROM emp;
ENAME TO_CHAR(
---------- --------
SMITH 17/12/80
ALLEN 20/02/81
WARD 22/02/81
JONES 02/04/81
MARTIN 28/09/81
BLAKE 01/05/81
CLARK 09/06/81
SCOTT 19/04/87
KING 17/11/81
TURNER 08/09/81
ADAMS 23/05/87
ENAME TO_CHAR(
---------- --------
JAMES 03/12/81
FORD 03/12/81
MILLER 23/01/82
已选择14行。
SQL> select ename,to_char(hiredate,'yy') FROM emp;
ENAME TO
---------- --
SMITH 80
ALLEN 81
WARD 81
JONES 81
MARTIN 81
BLAKE 81
CLARK 81
SCOTT 87
KING 81
TURNER 81
ADAMS 87
ENAME TO
---------- --
JAMES 81
FORD 81
MILLER 82
已选择14行。
SQL>是的，大小写都行。
-----------
fm用于压缩空格与去掉前导0
SQL> select to_char(SYSDATE,'fmDD MONTH YEAR') FROM dual;
TO_CHAR(SYSDATE,'FMDDMONTHYEAR')
----------------------------------------------------
2 4月 TWENTY EIGHTEEN
SQL> select to_char(SYSDATE,'DD MONTH YEAR') FROM dual;
TO_CHAR(SYSDATE,'DDMONTHYEAR')
----------------------------------------------------
02 4月 TWENTY EIGHTEENfm:(format_model)日期格式化模式。
col hiredate for a60:将hiredate的输出宽度加长为60个字符。
SQL> help col
COLUMN
------
Specifies display attributes for a given column, such as:
- text for the column heading
- alignment for the column heading
- format for NUMBER data
- wrapping of column data
Also lists the current display attributes for a single column
or all columns.
COL[UMN] [{column | expr} [option ...] ]
where option represents one of the following clauses:
ALI[AS] alias
CLE[AR]
ENTMAP {ON|OFF}
FOLD_A[FTER]
FOLD_B[EFORE]
FOR[MAT] format
HEA[DING] text
JUS[TIFY] {L[EFT] | C[ENTER] | R[IGHT]}
LIKE {expr | alias}
NEWL[INE]
NEW_V[ALUE] variable
NOPRI[NT] | PRI[NT]
NUL[L] text
OLD_V[ALUE] variable
ON|OFF
WRA[PPED] | WOR[D_WRAPPED] | TRU[NCATED]
SQL>SQL> col hiredate for a60
SQL> select ename "Name",dal "Salary",
2 to_char(hiredate,'fmDdspth "of" Month Year fmHH:MI:SS AM') HIREDATE
3 FROM emp;
select ename "Name",dal "Salary",
*
第 1 行出现错误:
ORA-00904: "DAL": 标识符无效
SQL> 1
1* select ename "Name",dal "Salary",
SQL> change /dal/sal
1* select ename "Name",sal "Salary",
SQL> /
Name Salary
---------- ----------
HIREDATE
------------------------------------------------------------
SMITH 800
Seventeenth of 12月 Nineteen Eighty 12:00:00 上午
ALLEN 1600
Twentieth of 2月 Nineteen Eighty-One 12:00:00 上午
WARD 1250
Twenty-Second of 2月 Nineteen Eighty-One 12:00:00 上午
Name Salary
---------- ----------
HIREDATE
------------------------------------------------------------
JONES 2975
Second of 4月 Nineteen Eighty-One 12:00:00 上午
MARTIN 1250
Twenty-Eighth of 9月 Nineteen Eighty-One 12:00:00 上午
BLAKE 2850
First of 5月 Nineteen Eighty-One 12:00:00 上午
Name Salary
---------- ----------
HIREDATE
------------------------------------------------------------
CLARK 2450
Ninth of 6月 Nineteen Eighty-One 12:00:00 上午
SCOTT 3000
Nineteenth of 4月 Nineteen Eighty-Seven 12:00:00 上午
KING 5000
Seventeenth of 11月 Nineteen Eighty-One 12:00:00 上午
Name Salary
---------- ----------
HIREDATE
------------------------------------------------------------
TURNER 1500
Eighth of 9月 Nineteen Eighty-One 12:00:00 上午
ADAMS 1100
Twenty-Third of 5月 Nineteen Eighty-Seven 12:00:00 上午
JAMES 950
Third of 12月 Nineteen Eighty-One 12:00:00 上午
Name Salary
---------- ----------
HIREDATE
------------------------------------------------------------
FORD 3000
Third of 12月 Nineteen Eighty-One 12:00:00 上午
MILLER 1300
Twenty-Third of 1月 Nineteen Eighty-Two 12:00:00 上午
已选择14行。
===========
to_char(number,'fmt')
https://blog.csdn.net/qq_34907701/article/details/79786811
常用的模式：
9：不显示前导0的一位数字
0：显示前导0的一位数字
$:显示美元符
L：本地货币
.:显示小数点
，：显示千位符
MI：在数的右边显示减号
PR：把负数用尖括号括起来
SQL> select ename "Name",to_char(sal*12,'$99,999.00') "annual salary" from emp;
Name annual sala
---------- -----------
SMITH $9,600.00
ALLEN $19,200.00
WARD $15,000.00
JONES $35,700.00
MARTIN $15,000.00
BLAKE $34,200.00
CLARK $29,400.00
SCOTT $36,000.00
KING $60,000.00
TURNER $18,000.00
ADAMS $13,200.00
Name annual sala
---------- -----------
JAMES $11,400.00
FORD $36,000.00
MILLER $15,600.00
已选择14行。
SQL> select ename "Name",to_char(sal*12,'$999.00') "annual salary" from emp;
Name annual s
---------- --------
SMITH ########
ALLEN ########
WARD ########
JONES ########
MARTIN ########
BLAKE ########
CLARK ########
SCOTT ########
KING ########
TURNER ########
ADAMS ########
Name annual s
---------- --------
JAMES ########
FORD ########
MILLER ########
已选择14行。
SQL>
注意位数要留够。否则就会显示为####了。
SQL> select ename "Name",to_char(sal*12,'L99,999.00') "annual salary" from emp;
Name annual salary
---------- --------------------
SMITH ￥9,600.00
ALLEN ￥19,200.00
WARD ￥15,000.00
JONES ￥35,700.00
MARTIN ￥15,000.00
BLAKE ￥34,200.00
CLARK ￥29,400.00
SCOTT ￥36,000.00
KING ￥60,000.00
TURNER ￥18,000.00
ADAMS ￥13,200.00
Name annual salary
---------- --------------------
JAMES ￥11,400.00
FORD ￥36,000.00
MILLER ￥15,600.00
已选择14行。to_number(str [,fmt]')
to_date(str [,fmt]')