第10章 单行函数
可以将函数广泛的分为单行函数和多行函数
select * from test3 order by tnum desc
select bdz_id, shebei_id, shebei_name, user_id
from tf_dev_ctrl
where bdz_id = &BDZID
order by bdz_id, user_id desc
select bdz_id, mingzi, &&col
from tf_substation
where mingzi is not null
order by &col
select bdz_id , mingzi, length(mingzi) as length
from tf_substation
lower(s) s代表字符串 小写
upper(s) s代表字符串 大写
initcap(s) 首字母大写
concat(s1,s2) 连接两个字符串
length(s) 字符数
lpad(s,n,p) rpad(s,n,p)
select initcap('hello world') from dual
//Hello World
select concat('today is:',sysdate) from dual
//Today Is:22-12月-17
select lpad('12',5,'02') lad from dual
//02012
select rpad('12',5,'02') lad from dual
//12020
select trim(both '*' from '****hiddle******') trims from dual
//hiddle
select trim(leading '*' from '****hiddle******') trims from dual
//hiddle******
select trim(trailing '*' from '****hiddle******') trims from dual
****hiddle
select instr('1#3#5#7','#') from dual //2
select instr('1#3#5#7','#',5) from dual //6
select instr('1#3#5#7#9#','#',3,4) from dual
//10 位置3开始第四次出现位置为10
instr和substr配合使用，从电子数据流中提取已编码的数据
select substr('1#3#5#7#9#',5) from dual //5#7#9#
select substr('1#3#5#7#9#',5,3) from dual //5#7
select substr('1#3#5#7#9#',-3,3) from dual //#9#
select replace('1#3#5#7#9#','#') from dual //13579
select replace('1#3#5#7#9#','#','->') from dual //1->3->5->7->9->
select round(1601.916,1) from dual //1601.9
select round(1601.916,2) from dual //1601.92
select round(1601.916,-3) from dual //2000
select round(1601.916) from dual //1602
select trunc(1601.916,1) from dual //1601.9
select trunc(1601.916,2) from dual //1601.91
select trunc(1601.916,-3) from dual //1000
select trunc(1601.916) from dual //1601
select mod(6,2) from dual //0
select mod(5,3) from dual //2
select mod(7,35) from dual //7
select mod(5.2,3) from dual //2.2
所有偶数除以2都没有余数，但是奇数除以2的余数是1。
因此mod函数用来区分偶数和奇数。
select months_between(sysdate,sysdate-31)*31 from dual
两个日期之间月份的差值，以31天算。
add_months(startdate,number) 月份加number
返回给定日期的最后一天
select last_day(sysdate) from dual
sysdate=2017/12/22 16:07:18
返回2017/12/31 16:07:18
select substr('zyb@gmail.com',
instr('zyb@gmail.com', '@') + 1,
instr('zyb@gmail.com', '.com')
- instr('zyb@gmail.com', '@') - 1) mail
from dual --gmail
to_number函数将字符转化成数字，
to_number(123.56,'999.9')返回错误，
to_char(123.56,'999.9')返回123.6
select nvl(null,1234) from dual //1234
nvl函数可用于将null的数字值转化成0
select nvl2(12,123,456) from dual//123
select nvl2(null,123,456) from dual//456
nullif(123,123) //返回空
nullif(123,456) //返回123
相等返回空，不相等返回第一项
nvl(original,ifnull)非空返回original,空返回ifnull
nvl2(original,ifnotnull,ifnull)
coalesce(p1,p2,..)返回第一个非空的值。p1,p2必须。
select decode('search','com1','true1','com2','true2','search','true3','iffalse')
返回true3.
select case substr(1234, 1, 3)
when '134' then
'1234 is match'
when '1235' then
'1235 is match'
when concat('1', '23') then
concat('1', '23') || ' is match'
end
from dual //123 is match