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副标题[/!--empirenews.page--]
基本
--新建表：
create table table1( id varchar(300) primary key,name varchar(200) not null);
--插入数据
insert into table1 (id,name) values (‘aa‘,‘bb‘);
--更新数据
update table1 set id = ‘bb‘ where id=‘cc‘;
--删除数据
delete from table1 where id =‘cc‘;
--删除表
drop table table1;
--修改表名：
alter table table1 rename to table2;
--表数据复制：
insert into table1 (select * from table2);
--复制表结构：
create table table1 select * from table2 where 1>1;
--复制表结构和数据：
create table table1 select * from table2;
--复制指定字段：
create table table1 as select id,name from table2 where 1>1;
--条件查询：
select id,name (case gender when 0 then ‘男‘ when 1 then ‘女’ end ) gender from table1
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(-1,9) 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;
rownum相关
--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 * from (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)t where rownum<9 )p where p.rn>6;--效率远高于方式一
?分页查询
（假设每页显示10条）
不包含排序：
--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;
包含排序：
--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 ( select d.* from DJDRIVER d order by DJDRIVER_DRIVERTIMES)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)t where rownum<=20 )p where p.rn>=10;
?时间处理
1. to_char和to_date基本使用
--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
eg1:
select to_char(sysdate,‘yyyy-mm-dd hh24:mi:ss‘)currenttime,
to_char(sysdate,‘yyyy‘) year,‘mm‘) month,‘dd‘) day,‘day‘) week,‘hh24‘)hour,‘mi‘) minute,‘ss‘) second
from dual;
eg2:
select to_date(‘2009-07-04 05:02:01‘,
to_char(to_date(‘2009-07-04 05:02:01‘,‘yyyy-mm-dd hh24:mi:ss‘),‘yyyy‘)year,‘mm‘)month,‘day‘,‘NLS_DATE_LANGUAGE=American‘) week,--设置语言
to_char(to_date(‘2009-07-04 05:02:01‘,‘ss‘) second
from dual;
2）months_between
select months_between(to_date(‘03-31-2014‘,‘MM-DD-YYYY‘),to_date(‘12-31-2013‘,‘MM-DD-YYYY‘)) "MONTHS"
FROM DUAL;
3)next_day
select sysdate today,next_day(sysdate,6) nextweek from dual;
4)时间区间
例：
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‘);
5）interval
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;
6）add_months
select add_months(sysdate,12) newtime from dual;
7)extract
select extract(month from sysdate) "This Month",
extract(year from add_months(sysdate,36)) " Years" from dual;
字符函数
--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‘,‘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
from dual;
to_number
--to_number(expr)
--to_number(expr,format)
--to_number(expr,format,‘nls-param‘)
select to_number(‘0123‘)number1,--converts a string to number
trunc(to_number(‘0123.123‘),2) number2,
to_number(‘120.11‘,‘999.99‘) number3,
to_number(‘0a‘,‘xx‘) number4,--converts a hex number to decimal
to_number(100000,‘xxxxxx‘) number5
from dual;
聚合函数
student表如下：
count：
--count (distinct|all)
select count(1) as count from student;--效率最高
select count(*) as count from student;
select count(distinct score) from student;
语句1结果：11
avg
--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;
语句3输出结果：
?
max
--max (distinct|all)
select max(score) from student;
select classno,max(score) score from student group by classno;
min
--min (distinct|all)
select min(score) from student;
select classno,min(score) score from student group by classno;
stddev（standard deviation）标准差
--stddev
select stddev(score) from student;
select classno,stddev(score) score from student group by classno;
sum
--sum
select sum(score) from student;
select classno,sum(score) score from student group by classno;
median--中位数
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