本文包括字符函数,数学函数。日期函数,聚合函数,伪列rownum,分页查询
字符函数
select substr('abcdefg',1,5)substr, --字符串截取
instr('abcdefg','bc') instr, --查找子串
'Hello'||'World' concat, --连接
trim(' wish ') trim, --去前后空格
rtrim('wish ') rtrim, --去后面空格
ltrim(' wish') ltrim, --去前面空格
trim(leading 'w' from 'wish') deleteprefix, --去前缀
trim(trailing 'h' from 'wish') deletetrailing, --去后缀
trim('w' from 'wish') trim1,
ascii('A') A1,
ascii('a') A2, --ascii(转换为对应的十进制数)
chr(65) C1,
chr(97) C2, --chr(十进制转对应字符)
length('abcdefg') len, --length
lower('WISH')lower,
upper('wish')upper,
initcap('wish')initcap, --大小写变换
replace('wish1','1','youhappy') replace, --替换
translate('wish1','1','y')translate, --转换,对应一位(前面的位数大于等于后面的位数)
translate('wish1','sh1','hy')translate1,
concat('11','22') concat --连接
wm_concat('列1','列2') --列名合并
from dual;
select to_number('0123')number1, --转化字符串到数字
trunc(to_number('0123.123'),2) number2,
to_number('120.11','999.99') number3,
to_number('0a','xx') number4, --转化十六进制到十进制
to_number(100000,'xxxxxx') number5
from dual;
数学函数
--绝对值: abs()
select abs(-2) value from dual; --(2)
--取整函数(大): ceil()
select ceil(-2.001) value from dual; --(-2)
--取整函数(小): floor()
select floor(-2.001) value from dual; --(-3)
--取整函数(截取): trunc()
select trunc(-2.001) value from dual; -- (-2)
--四舍五入: round()
select round(1.234564,4) value from dual; --(1.2346)
--取平方:Power(m,n)
select power(4,2) value from dual; --(16)
--取平方根:SQRT()
select sqrt(16) value from dual; --(4)
--取随机数: dbms_random(minvalue,maxvalue)
select dbms_random.value() from dual; (默认是0到1之间)
select dbms_random.value(2,4) value from dual; (2-4之间随机数)
--取符号: Sign()
select sign(-3) value from dual; --(-1)
select sign(3) value from dual; --(1)
--取集合的最大值: greatest(value)
select greatest(-1,3,5,7,9) value from dual; --(9)
--取集合的最小值: least(value)
select least(-1,3,5,7,9) value from dual; --(-1)
--处理Null值: nvl(空值,代替值)
select nvl(null,10) value from dual; --(10)
select nvl(score,10) score from student;
日期函数
--日期
--年 yyyy yyy yy year
--月 month mm mon month
--日+星期 dd ddd(一年中第几天) dy day
--小时 hh hh24
--分 mi
--秒 ss
select to_char(sysdate,'yyyy-mm-dd hh24:mi:ss')currenttime,
to_char(sysdate,'yyyy') year,
to_char(sysdate,'mm') month,
to_char(sysdate,'dd') day,
to_char(sysdate,'day') week,
to_char(sysdate,'hh24')hour,
to_char(sysdate,'mi') minute,
to_char(sysdate,'ss') second
from dual;
select to_date('2009-07-04 05:02:01','yyyy-mm-dd hh24:mi:ss')currenttime,
to_char(to_date('2009-07-04 05:02:01','yyyy-mm-dd hh24:mi:ss'),'yyyy')year,
to_char(to_date('2009-07-04 05:02:01','yyyy-mm-dd hh24:mi:ss'),'mm')month,
to_char(to_date('2009-07-04 05:02:01','yyyy-mm-dd hh24:mi:ss'),'dd') day,
to_char(to_date('2009-07-04 05:02:01','yyyy-mm-dd hh24:mi:ss'),'day') week,
to_char(to_date('2009-07-04 05:02:01','yyyy-mm-dd hh24:mi:ss'),'day','NLS_DATE_LANGUAGE=American') week, --设置语言
to_char(to_date('2009-07-04 05:02:01','yyyy-mm-dd hh24:mi:ss'),'hh24')hour,
to_char(to_date('2009-07-04 05:02:01','yyyy-mm-dd hh24:mi:ss'),'mi') minute,
to_char(to_date('2009-07-04 05:02:01','yyyy-mm-dd hh24:mi:ss'),'ss') second
from dual;
--months_between
select months_between(to_date('03-31-2014','MM-DD-YYYY'),to_date('12-31-2013','MM-DD-YYYY')) "MONTHS"
FROM DUAL;
--next_day
select sysdate today, next_day(sysdate,6) nextweek from dual;
--时间区间
select cardid, borrowdate from borrow where to_date(borrowdate,'yyyy-mm-dd hh24:mi:ss')
between
to_date('2014-02-01 00:00:00','yyyy-mm-dd hh24:mi:ss') and
to_date('2014-05-01 00:00:00','yyyy-mm-dd hh24:mi:ss');
--interval 间隔
select to_char(sysdate,'yyyy-mm-dd hh24:mi:ss') currenttime,
to_char(sysdate - interval '7' year,'yyyy-mm-dd hh24:mi:ss') intervalyear,
to_char(sysdate - interval '7' month,'yyyy-mm-dd hh24:mi:ss') intervalMonth,
to_char(sysdate - interval '7' day,'yyyy-mm-dd hh24:mi:ss') intervalday,
to_char(sysdate - interval '7' hour,'yyyy-mm-dd hh24:mi:ss') intervalHour,
to_char(sysdate - interval '7' minute,'yyyy-mm-dd hh24:mi:ss') intervalMinute,
to_char(sysdate - interval '7' second,'yyyy-mm-dd hh24:mi:ss') intervalSecond
from dual;
--add_months 增加月份
select add_months(sysdate,12) newtime from dual;
--extract
select extract(month from sysdate) "This Month", --当前月
extract(year from add_months(sysdate,36)) " Years" from dual; --当前年份+3
聚合函数
--count
select count(1) as count from student;--效率最高
select count(*) as count from student;
select count(distinct score) from student;
--avg
--distinct|all
select avg(score) score from student;
select avg(distinct score) from student;
select classno,avg(score) score from student group by classno;
--max
--distinct|all
select max(score) from student;
select classno, max(score) score from student group by classno;
--min
--distinct|all
select min(score) from student;
select classno, min(score) score from student group by classno;
--stddev(standard deviation)标准差
select stddev(score) from student;
select classno, stddev(score) score from student group by classno;
--sum
select sum(score) from student;
select classno, sum(score) score from student group by classno;
--median--中位数
select median(score) from student;
select classno, median(score) score from student group by classno;
伪列rownum
--rownum小于某个数时可以直接作为查询条件(注意oracle不支持select top)
select * from student where rownum <3;
--查询rownum大于某个数值,需要使用子查询,并且rownum需要有别名
select * from(
select rownum rn ,id,name from student
)
where rn>2;
select rownum rn, student.* from student
where rn >3;
--区间查询
select * from (
select rownum rn, student.* from student)
where rn >3 and rn<6;
--排序+前n条
select * from (
select rownum rn, t.* from (
select d.* from DJDRUVER d order by drivernumber)t
)p where p.rn<10;
--排序+区间查询1
select * from (
select rownum rn, t.* from (
select d.* from DJDRIVER d order by DJDRIVER_DRIVERTIMES
)t
)p where p.rn<9 and p.rn>6;
--排序+区间查询2
select * from (
select rownum rn, t.* from (
select d.* from DJDRIVER d order by DJDRIVER_DRIVERTIMES
where rownum<9
where p.rn>6;--效率远高于方式一
分页查询
--假设每页显示10条
--效率低
select * from (
select rownum rn, d.* from DJDRIVER d )p
where p.rn<=20 and p.rn>=10;
select * from (
select rownum rn, d.* from DJDRIVER d )p
where p.rn between 10 and 20;
--效率高
select * from (
select rownum rn, d.* from DJDRIVER d where rownum<=20 )p
where p.rn>=10;
--排序+区间查询1(效率低)
select * from (
select rownum rn, t.* from (
select d.* from DJDRIVER d order by DJDRIVER_DRIVERTIMES
)t
)p
where p.rn<=20 and p.rn>=10;
select * from (
select rownum rn, t.* from (
)t
)p
where p.rn between 10 and 20;
--排序+区间查询2(效率高)
select * from (
select rownum rn, t.* from (
select d.* from DJDRIVER d order by DJDRIVER_DRIVERTIMES
where rownum<=20
)p
where p.rn>=10;
分析函数 --over
分组取前三
SELECT t.*
FROM (SELECT ROW_NUMBER() OVER (PARTITION BY 分组条件 ORDER BY 排序规则 DESC) rn,
b.*
FROM 表名 b) t
WHERE t.rn <= 3;
select d.* ,Rank() Over(partition by d.分组条件 order by d.排序规则 desc) mm from 表名 d;