Oracle读书笔记(一)

sqlplus sys/所设定的密码 as sysdba(用管理员登陆)
alter user scott account unlock;(解锁scott账户)

1. table structure

描述某一张表：desc 表名
select * from 表名

2. select 语句

  计算数据可以用空表：比如：select 2*3 from dual

  select ename,sal*12 annual_sal from emp;与select ename,sal*12 "annual sal" from emp;区别，加双引号保持原大小写。不加全变大写。

  select ename || "abcd" 如果连接字符串中含有单引号，用两
4000
个单引号代替一个单引号。(||代表连接符)

3. distinct

   select deptno from emp;
   select distinct deptno from emp;
​
   select distinct deptno from emp;
   select distinct deptno ,job from emp
   去掉deptno,job两者组合的重复。更多的项，就是这么多项的组合的不重复组合。

4. where

   select * from emp where deptno =10;
   select * from emp where deptno <>10;不等于10      
   select * from emp where ename ='bike';
   select ename,sal from emp where sal between 800 and 1500 (>=800 and <=1500)空值处理:
   select ename,sal,comm from emp where comm is (not) null;
   select ename,sal,comm from emp where ename ( not)in ('smith','king','abc');
   select ename from emp where ename like '_A%';_代表一个字母,%代表0个或多个字母. 如果查询%
   可用转义字符.\%. 还可以用escape '$'比如:select ename from emp where ename like '%$a%' escape '$';

5. orderby

    select * from dept;
    select * from dept order by dept desc;(默认:asc)
    select ename,sal,deptno from emp order by deptno asc,ename desc;

6. sql function1

   select ename,sal*12 annual_sal from emp
   where ename not like '_A%' and sal>800
   order by sal desc;
​
   select lower(ename) from emp;
​
   select ename from emp
   where lower(ename) like '_a%';等同于
   select ename from emp where ename like '_a%' or ename like '_A%';
​
   select substr(ename,2,3) from emp;从第二字符截,一共截三个字符.
   select chr(65) from dual 结果为:A
   select ascii('a') from dual 结果为:65
   select round(23.652,1) from dual; 结果为: 23.7
   select round(23.652,-1) from dual; 20

   select to_char(sal,'$99_999_999') from emp;
   select to_char(sal,'L99_999_999') from emp;人民币符号,L:代表本地符号
​
   这个需要掌握牢:
   select birthdate from emp;
   显示为:
   BIRTHDATE
   ----------------
   17-12月-80
   ----------------
​
   改为:
   select to_char(birthdate,'YYYY-MM-DD HH:MI:SS') from emp;
 
   显示:
   
   BIRTHDATE
   -------------------
   1980-12-17 12:00:00
   -------------------
 
   select to_char(sysdate,'YYYY-MM-DD HH24:MI:SS') from dual; //也可以改为:HH12
   TO_CHAR(SYSDATE,'YY
   -------------------
   2017-07-15 14:46:14

   to_date函数:
   select ename,birthdate from emp where birthdate > to_date('1981-2-20 12:34:56','YYYY-MM-DD HH24:MI:SS');
   如果直接写 birthdate>'1981-2-20 12:34:56'会出现格式不匹配,因为表中的格式为: DD-MM月-YY.

   select sal from emp where sal>888.88 无错.但
   select sal from emp where sal>$1,250,00;
   会出现无效字符错误.
   改为:
   select sal from emp where sal>to_number('$1,250.00','$9,999.99');s
 
   把空值改为0
   select ename,sal*12+nvl(comm,0) from emp;
   这样可以防止comm为空时,sal*12相加也为空的情况.

7. Group function 组函数

   max,min,avg ,count,sum函数

   select to_char(avg(sal),'99999999,99') from emp;    

   select round(avg(sal),2) from emp;
   结果:2073.21
   
   select count(*) from emp where deptno=10;
   select count(ename) from emp where deptno=10; count某个字段,如果这个字段不为空就算一个.
   select count(distinct deptno) from emp;
   select sum(sal) from emp;

前言

sqlplus sys/所设定的密码 as sysdba(用管理员登陆)
alter user scott account unlock;(解锁scott账户)

1. table structure

描述某一张表：desc 表名
select * from 表名

2. select 语句

  计算数据可以用空表：比如：select 2*3 from dual

  select ename,sal*12 annual_sal from emp;与select ename,sal*12 "annual sal" from emp;区别，加双引号保持原大小写。不加全变大写。 

  select ename || "abcd" 如果连接字符串中含有单引号，用两个单引号代替一个单引号。(||代表连接符)

3. distinct

   select deptno from emp;
   select distinct deptno from emp;
​
   select distinct deptno from emp;
   select distinct deptno ,job from emp
   去掉deptno,job两者组合的重复。更多的项，就是这么多项的组合的不重复组合。

4. where

   select * from emp where deptno =10;
   select * from emp where deptno <>10;不等于10      
   select * from emp where ename ='bike';
   select ename,sal from emp where sal between 800 and 1500 (>=800 and <=1500)空值处理:
   select ename,sal,comm from emp where comm is (not) null;
   select ename,sal,comm from emp where ename ( not)in ('smith','king','abc');
   select ename from emp where ename like '_A%';_代表一个字母,%代表0个或多个字母. 如果查询%
   可用转义字符.\%. 还可以用escape '$'比如:select ename from emp where ename like '%$a%' escape '$';

5. orderby

    select * from dept;
    select * from dept order by dept desc;(默认:asc)
    select ename,sal,deptno from emp order by deptno asc,ename desc;

6. sql function1

   select ename,sal*12 annual_sal from emp
   where ename not like '_A%' and sal>800
   order by sal desc;
​
   select lower(ename) from emp;
​
   select ename from emp
   where lower(ename) like '_a%';等同于
   select ename from emp where ename like '_a%' or ename like '_A%';
​
   select substr(ename,2,3) from emp;从第二字符截,一共截三个字符.
   select chr(65) from dual 结果为:A
   select ascii('a') from dual 结果为:65
   select round(23.652,1) from dual; 结果为: 23.7
   select round(23.652,-1) from dual; 20

   select to_char(sal,'$99_999_999') from emp;
   select to_char(sal,'L99_999_999') from emp;人民币符号,L:代表本地符号
​
   这个需要掌握牢:
   select birthdate from emp;
   显示为:
   BIRTHDATE
   ----------------
   17-12月-80
   ----------------
​
   改为:
   select to_char(birthdate,'YYYY-MM-DD HH:MI:SS') from emp;
 
   显示:
   
   BIRTHDATE
   -------------------
   1980-12-17 12:00:00
   -------------------
 
   select to_char(sysdate,'YYYY-MM-DD HH24:MI:SS') from dual; //也可以改为:HH12
   TO_CHAR(SYSDATE,'YY
   -------------------
   2017-07-15 14:46:14

   to_date函数:
   select ename,birthdate from emp where birthdate > to_date('1981-2-20 12:34:56','YYYY-MM-DD HH24:MI:SS');
   如果直接写 birthdate>'1981-2-20 12:34:56'会出现格式不匹配,因为表中的格式为: DD-MM月-YY. 

   select sal from emp where sal>888.88 无错.但
   select sal from emp where sal>$1,250,00;
   会出现无效字符错误.
   改为:
   select sal from emp where sal>to_number('$1,250.00','$9,999.99');s
 
   把空值改为0
   select ename,sal*12+nvl(comm,0) from emp;
   这样可以防止comm为空时,sal*12相加也为空的情况.

7. Group function 组函数

   max,min,avg ,count,sum函数 

   select to_char(avg(sal),'99999999,99') from emp;    

   select round(avg(sal),2) from emp;
   结果:2073.21
   
   select count(*) from emp where deptno=10;
   select count(ename) from emp where deptno=10; count某个字段,如果这个字段不为空就算一个.
   select count(distinct deptno) from emp;
   select sum(sal) from emp;