20200225
First, one-way function
1, character function
Case Control Functions: lower (), upper (), initcap ()
select lower ( 'HELLO') from dual; HELLO temporary table for converting characters to lowercase
lower (), upper (), initcap () is changed each word
select upper ( 'Welcome welcome to Chinese china') from dual;
2, character control function
concat () connect function
select concat(ename,job) from emp;
select ename || job from emp;
substr () function interception
select sustr ( 'hello, world', 1,5) form dual; from hello, world's first character string beginning interception, intercept length of 5, returns hello
length () function character length
select length ( 'hello, world') form dual; read length of the string
lpad / rpad character left / right padding function
select empno, lpad emp (ename, 10, '*') from; bits when not performing interception function
trim () function truncates inclusive
select trim ( 'aa bb') from dual; removing the leading and trailing spaces, the intermediate spaces reserved
select ltrim ( 'aa bb') from dual; removing the first space (left start) (This can be written only remove spaces), the remaining space reserved
trim (leading | trailing | both) removed from the front | back | front
select ename, trim ( 'A' from ename) from emp; ename remove characters inclusive of A, nothing is written, both default
select trim(trailing 'a' from 'aadfaa aasda') from dual; 返回字符串'aadfaa aasd'
taken in the trim value, only a character
select ltrim ( 'aabbccddaabb', 'ab') from dual; a and b are removed from the left character string, if the character does not return the original
instr () function to find
select ename, instr (ename, 'BE') from emp; Where to Find ename contains characters BE, and returns the first occurrence
select instr('hello world','or',5) from dual;
select instr ( 'hello world', 'o', 1,1) from dual; return to the first position of the first occurrence o
select instr ( 'hello world', 'o', 1,2) from dual; 2 returns the position of the first occurrence of o
select ename from emp where ename not like '% R%'; no query name with the employee name R
select ename from emp where instr (ename, 'R') = 0; no query name with the employee name R
replace () Replace single character
replace (value, str1, str2) replaces the value of the str1 str2
select ename, replace from emp (ename, 'A', 'a'); A in the name are replaced with a
translate () a plurality of character substitutions
More space than replace
select ename,translate(ename,'AS','as') from emp; 将姓名中的A替换为a,S替换为s
select ename,translate(ename,'AS','a') from emp; 将姓名中的A替换为a,S去掉
周杰伦→**伦,把最后一个字前面的字都提取出来,然后用*去替换掉
select translate('周杰伦',substr('周杰伦',1,length('周杰伦')-1),'********') from dual; //**伦
select translate('成龙',substr('成龙',1,length('成龙')-1),'********') from dual; //**龙
select translate('布莱恩特',substr('布莱恩特',1,length('布莱恩特')-1),'********') from dual; //***特
3、数字函数
round()四舍五入函数、trunc()截断函数、mod()求余函数
round(45.926,2)=45.93 round(45.926,-1)=50
trunc(45.926,2)=45.92 trunc(45.926,-1)=40
mod(10,3)=1(10/3=3......1)
4、日期函数
sysdate返回当前日期
日期-数字=日期 日期+数字=日期 日期-日期=数字(间隔天数)
months_between返回两个日期间隔的月数
select months_between(sysdate,hiredate) from emp查询每个员工入职的月数
add_months(sysdate,2) 返回当前日期+2月后的日期
next_day(sysdate,'星期一')返回当前日期后的下个星期一的日期,星期几怎么书写需要视当前的字符编码集,中文则输入星期几,英文则输入monday等。
last_day(sysdate) 返回当前日期所在月份的最后一天
select last_day('01-2月-2008'),last_day(sysdate) from dual; //29-2月 -08 29-2月 -20
5、转换函数
to_number()把其他类型转换成数字,目前已实现自动转换 不需使用函数
select 1+1,'1'+1 from dual; //2 2
to_date()把其他类型转换成日期
select to_date('2020-02-25','yyyy-mm-dd') from dual; //25-2月 -20
to_char()把其他类型转换成字符串
select to_char(sysdate,'yyyy"年"mm"月"dd"日"') from dual; //2020-02-25
把当前日期转换成年月日的中文格式:
select to_char(sysdate,'yyyy"年"mm"月"dd"日"') from dual; //2020年02月25日
select to_char(sysdate,'yyyy')||'年'||to_number(to_char(sysdate,'mm'))||'月'||to_number(to_char(sysdate,'dd'))||'日' from dual; //2020年02月25日
注:字符串当中,存在 自定义的字符信息的时候,需要使用双引号 标记那些 直接显示 而不需要额外处理的字符
select to_char(sysdate,'fmyyyy"年"mm"月"dd"日"') from dual; //2020年2月25日,fm去除前导0
select to_char(sysdate,'fmyyyy-mm-dd hh24:mi:ss am') from dual; //2020-2-25 16:20:58 下午
select to_char(sysdate,'fmyyyy-mm-dd am hh24:mi') from dual; //2020-2-25下午16:20:58
美元按照默认格式,会将¥放到数额前面;其他货币是外挂上去的,会按照定义格式写
select ename,to_char(sal,'99,999$'),to_char(sal,'99,999L') from emp; //KOBE $4,000 4,000¥
select ename,to_char(sal,'99g999$'),to_char(sal,'99G999L') from emp;//KOBE $4,000 4,000¥
select add_months(sysdate,1) from dual; //当前日期+1月
select sysdate,sysdate+7 from dual; //当前日期+1周
select sysdate,sysdate+1 from dual; //当前日期+1天
select sysdate,to_char(sysdate+1/24,'yyyy-mm-dd am hh24:mi:ss') from dual; //当前日期+1时
select to_char(sysdate+1/24/60,'yyyy-mm-dd am hh24:mi:ss') from dual; //当前日期+1分
select to_char(sysdate+1/24/60/60,'yyyy-mm-dd am hh24:mi:ss') from dual; //当前日期+1秒
select to_char(sysdate,'yyyy"年"mm"月"dd"日" "第"W"周"') from dual; //2020年02月25日 第4周
select to_char(sysdate,'d'),to_char(sysdate,'day'),to_char(sysdate,'w') from dual; //d表示今天是本周的第几天(周日是第一天),day表示今天是星期几,w表示这是本月的第几周。
作者:kerwin-chyl
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