oracle培训老师笔记.doc
oracle笔记 (2008-10-30 10:17:39) 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 '$'比如:select ename from emp where ename like '%$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),',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 )
