wishyouhappy

https://www.cnblogs.com/wishyouhappy/p/3700683.html#char

1）基本

2）數學函式

3）rownum

4）分頁

5）時間處理

6）字元函式

7）to_number

8）聚合函式

9）學生選課

10）圖書館借閱

 

基本

--新建表：
create table table1( id varchar(300) primary key, name varchar(200) not null);

--插入資料   
insert into table1 (id,name) values ('aa','bb');
 
--更新資料   
update
 
 table1 set id = 'bb' where id='cc';
 
--刪除資料   
delete from table1 where id ='cc';
 
--刪除表    
drop table table1;
 

--修改表名： 
alter table table1 rename to table2;
 
--表資料複製：
insert into table1 (select * from table2);
 
--複製表結構： 
create table table1 select * from table2 where 1>1;
 
--複製表結構和資料：
create
 
 table table1 select * from table2;
 
--複製指定欄位： 
create table table1 as select id, name from table2 where 1>1;

--條件查詢： 
select id,name (case gender when 0 then '男' when 1 then ‘女’ end  ) gender from  table1 
 

 

數學函式

--絕對值：abs()
   select abs(-2) value from dual;          --(2)

--取整函式（大）：ceil（）
   select ceil(-2.001) value from dual;       --(-2)

--取整函式（小）：floor（）
   select floor(-2.001) value from dual;       --(-3)

--取整函式（擷取）：trunc（）
   select trunc(-2.001) value from dual;       -- (-2)

--四捨五入：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)

--取隨機數:dbms_random(minvalue,maxvalue)
   select dbms_random.value() from dual;  (預設是0到1之間)
　select dbms_random.value(2,4) value from dual;  （2-4之間隨機數）

--取符號：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)

--處理Null值：nvl(空值，代替值)
   select  nvl(null,10) value from dual;       --(10)
　　
   select nvl(score,10) score from student;

 

 

 rownum相關

--rownum小於某個數時可以直接作為查詢條件（注意oracle不支援select top）
select * from student where rownum <3;

--查詢rownum大於某個數值,需要使用子查詢，並且rownum需要有別名
select * from(select rownum rn ,id,name from student) where rn>2;
select * from (select rownum rn, student.* from student) where rn >3;

--區間查詢
select * from (select rownum rn, student.* from student) where rn >3 and rn<6;

--排序+前n條
select * from (select rownum rn, t.* from ( select d.* from DJDRUVER d order  by drivernumber)t )p where p.rn<10;

--排序+區間查詢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+區間查詢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;--效率遠高於方式一

 

 分頁查詢

（假設每頁顯示10條）

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+區間查詢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+區間查詢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;

 

 時間處理

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(一年中第幾天) dy day 
--小時  hh hh24 
--分 mi
--秒 ss

eg1:

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;

eg2:

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, --設定語言
       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;

 

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)時間區間

eg：

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; 

 

 

字元函式

--字元函式
select substr('abcdefg',1,5)substr,                     --字串擷取
       instr('abcdefg','bc') instr,                     --查詢子串
       
       'Hello'||'World' concat,                         --連線
       
       trim('  wish  ') trim,                           --去前後空格
       rtrim('wish  ') rtrim,                           --去後面空格
       ltrim('  wish') ltrim,                           --去前面空格
       
       trim(leading 'w' from 'wish') deleteprefix,      --去字首
       trim(trailing 'h' from 'wish') deletetrailing,   --去後綴
       trim('w' from 'wish') trim1,
       
       ascii('A') A1, 
       ascii('a') A2,                                   --ascii(轉換為對應的十進位制數)
       chr(65) C1, 
       chr(97) C2,                                      --chr(十進位制轉對應字元)
       
       length('abcdefg') len,                           --length 
       
       lower('WISH')lower, 
       upper('wish')upper, 
       initcap('wish')initcap,                            --大小寫變換
       
       replace('wish1','1','youhappy') replace,           --替換
       
       translate('wish1','1','y')translate,               --轉換，對應一位(前面的位數大於等於後面的位數)
       translate('wish1','sh1','hy')translate1,
       
       concat('11','22') concat          　　　　　　　　   --連線


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;

 

 

聚合函式

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;     

語句1結果：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;

 

語句3輸出結果：

 

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）標準差

--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--中位數

--median
select median(score) from student;
select classno, median(score) score from student group by classno;

 

 案例1--學生選課

1. 建立表 stu（學生表），course（課程表），選課表（s_c）

--建立表

create table STU  
(  
  id   NUMBER not null,  
  name VARCHAR2(255)  
) ;
   
create table COURSE  
(  
  id  NUMBER not null,  
  coursename VARCHAR2(255)  
) ; 
   
create table S_C  
(  
  sid    NUMBER,  
  cid    NUMBER,  
  score NUMBER  
);

 

2.插入資料