Oracle基础知识点

第一课：客户端
1. Sql Plus(客户端），命令行直接输入：sqlplus，然后按提示输入用户名，密码。
2. 从开始程序运行:sqlplus，是图形版的sqlplus.
3. http://localhost:5560/isqlplus

    Toad：管理， PlSql Developer:

第二课：更改用户
1. sqlplus sys/bjsxt as sysdba
2. alter user scott account unlock;(解锁)

第三课：table structure

    1. 描述某一张表：desc 表名    2. select * from 表名

第四课：select 语句：

   1.计算数据可以用空表：比如：.select 2*3 from dual   2.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。   3. 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。

第五课：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。

第六课：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:selectenamefromempwhereenamelike′a%’ escape ‘$’;

第七课: 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;

第八课: 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    -------------------    2007-02-25 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');    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.

第九课: 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;

第十课: Group by语句

    需求:现在想求,求每个部门的平均薪水.    select avg(sal) from emp group by deptno;    select deptno avg(sal) from emp group by deptno;    select deptno,job,max(sal) from emp group by deptno,job;   求薪水值最高的人的名字.   select ename,max(sal) from emp;出错,因为max只有一个值,但等于max值的人可能好几个,不能匹配.   应如下求:   select ename from emp where sal=(select max(sal) from emp);   Group by语句应注意,   出现在select中的字段,如果没出现在组函数中,必须出现在Group by语句中.

第十一课: Having 对分组结果筛选

   Where是对单条纪录进行筛选,Having是对分组结果进行筛选.   select avg(sal),deptno from emp    group by deptno    having avg(sal)>2000;   查询工资大于1200雇员,按部门编号进行分组,分组后平均薪水大于1500,按工薪倒充排列.   select * from emp    where sal>1200   group by deptno   having avg(sal)>1500   order by avg(sal) desc;

第十二课:字查询

   谁挣的钱最多(谁:这个人的名字,  钱最多)   select 语句中嵌套select 语句,可以在where,from后.   问那些人工资,在平均工资之上.   select ename,sal from emp where sal>(select avg(sal) from emp);   查找每个部门挣钱最多的那个人的名字.   select ename ,deptno from emp where sal in(select max(sal) from ename group by deptno) 查询会多值.   应该如下:   select  max(sal),deptno from emp group by deptno;当成一个表.语句如下:   select ename, sal from emp join(select  max(sal) max_sal,deptno from emp group   by deptno) t on(emp.sal=t.max_sal and emp.deptno=t.deptno);    每个部门的平均薪水的等级.    分析:首先求平均薪水(当成表),把平均薪水和另外一张表连接.

第十四课:self_table_connection

   把某个人的名字以及他的经理人的名字求出来(经理人及这个人在表中同处一行)   分析:首先求出这个人的名字,取他的编号,然后从另一张表与其相对应编号,然后找到经理的名字.   select e1.ename ,e2.ename from emp e1,emp e2 where e1.mgr= e2.empno.   empno编号和MGR都是编号.

第十15课: SQL1999_table_connections

  select ename,dname,grade from emp e,dept d, sqlgrade s  where e.deptno = d.deptno and e.sql between s.losal and s.hisal and  job<>'CLERK';  有没有办法把过滤条件和连接条件分开来? 出于这样考虑,Sql1999标准推出来了.有许多人用的还是  旧的语法,所以得看懂这种语句.  select ename,dname from emp,dept;(旧标准).  select ename,dname from emp cross join dept;(1999标准)  select ename,dname from emp,dept where emp.deptno=dept.deptno (旧)   select ename,dname from emp join dept on(emp.deptno = dept.deptno); 1999标准.没有Where语句.  select ename,dname from emp join dept using(deptno);等同上句,但不推荐使用.  select ename,grade from emp e join salgrade s on(e.sal between s.losal and s.hisal);  join 连接语句, on过滤条件。连接，条件一眼分开。如果用Where语句较长时，连接语句和过滤语句混在一起。  三张表连接：  slect ename,dname, grade from   emp e join dept d on(e.deptno=d.deptno)  join salgrade s on(e.sal between s.losal and s.hisal)  where ename not like '_A%';  把每张表连接 条件不混在一起，然后数据过滤条件全部区分开来。读起来更清晰，更容易懂一点。  select e1.ename,e2.ename from emp e1 join emp e2 on(e1.mgr = e2.emptno);  左外连接：会把左边这张表多余数据显示出来。  select e1.ename,e2,ename from emp e1 left join emp e2 on(e1.mgr =e2.empno);left 后可加outer  右外连接：select ename,dname from emp e right outer join dept d on(e.deptno =d.deptno); outer可以取掉。  即把左边多余数据，也把右边多余数据拿出来，全外连接。  select ename,dname from emp e full join dept d on(e.deptno =d.deptno); 

16-23 课：求部门平均薪水的等级

   A.求部门平均薪水的等级。   select deptno,avg_sal,grade from    (select deptno,avg(sal) avg_sal from emp group by deptno)t   join salgrade s on(t.avg_sal between s.losal and s.hisal)   B.求部门平均的薪水等级   select deptno,avg(grade) from    (select deptno,ename, grade from emp join salgrade s on(emp.sal between s.losal and   s.hisal)) t   group by deptno   C.那些人是经理   select ename from emp where empno in(select mgr from emp);   select ename from emp where empno in(select distinct mgr from emp);   D.不准用组函数，求薪水的最高值（面试题）   select distinct sal from emp where sal not in(   select distinct e1.sal from emp e1 join emp e2 on (e1.sal<e2.sal));   E.平均薪水最高的部门编号   select deptno,avg_sal from   (select avg(sal)avg_sal,deptno from emp group by deptno)   where avg_sal=   (select max(avg_sal)from    (select avg(sal) avg_sal,deptno from emp group by deptno)   )   F.平均薪水最高的部门名称   select dname from dept where deptno=  (     select deptno from    (select avg(sal)avg_sal,deptno from emp group by deptno)    where avg_sal=    (select max(avg_sal)from     (select avg(sal) avg_sal,deptno from emp group by deptno)    )   )  G.求平均薪水的等级最低的部门的部门名称    组函数嵌套    如：平均薪水最高的部门编号，可以E.更简单的方法如下：    select deptno,avg_sal from     (select avg(sal) avg_sal,deptno from emp group by deptno)    where avg_sal =    (select max(avg(sal)) from emp group by deptno)    组函数最多嵌套两层    分析：    首先求    1.平均薪水： select avg(sal) from group by deptno;    2.平均薪水等级：  把平均薪水当做一张表，需要和另外一张表连接salgrade    select  deptno,grade avg_sal from       ( select deptno,avg(sal) avg_sal from emp group by deptno) t    join salgrade s on(t.avg_sal between s.losal and s.hisal)    上面结果又可当成一张表。    DEPTNO    GRADE    AVG_SAL  --------  -------  ----------    30           3   1566.66667    20           4   2175    10           4   2916.66667    3.求上表平均等级最低值    select min(grade) from    (      select deptno,grade,avg_sal from       (select deptno,avg(sal) avg_sal from emp group by deptno)t      join salgrade s on(t.avg_sal between s.losal and s.hisa)     )    4.把最低值对应的2结果的那张表的对应那张表的deptno, 然后把2对应的表和另外一张表做连接。      select dname ,deptno,grade,avg_sal from        (      select deptno,grade,avg_sal from          (select deptno,avg(sal) avg_sal from emp group by deptno)t         join salgrade s on(t.avg_sal between s.losal and s.hisal)         ) t1        join dept on (t1.deptno = dept.deptno)        where t1.grade =        (           select deptno,grade,avg_sal from           (select deptno,avg(sal) avg_sal from emp group by deptno) t            join salgrade s on(t.avg_sal between s.losal and s.hisal)           )        )     结果如下：    DNAME    DEPTNO     GRADE    AVG_SAL  --------  -------  --------   --------    SALES        30        3    1566.6667    H: 视图（视图就是一张表，一个字查询）   G中语句有重复，可以用视图来简化。   conn sys/bjsxt as sysdba;   grant create table,create view to scott;   conn scott/tiger   创建视图：   create view v$_dept_avg-sal_info as   select deptno,grade,avg_sal from    ( select deptno,avg(sal) avg_sal from emp group by deptno)t   join salgrade s on 9t.avg_sal between s.losal and s.hisal)   然后    select * from v$_dept_avg-sal_info   结果如下：   DEPTNO      GRADE    AVG_SAL  --------  -------  ----------    30           3   1566.66667    20           4   2175    10           4   2916.66667   然后G中查询可以简化成：   select  dname,t1.deptno,grade,avg_sal from   v$_dept_avg-sal_info t1   join dept on9t1.deptno =dept.deptno)   where t1.grade=   (select min(grade) from v$_dept_avg-sal_info t1   )