zoukankan      html  css  js  c++  java
  • Oracle笔记 三、function 、select

    Scott表下有这么几个常用的表,而且还带有数据。分别是emp、dept、salgrade;
    1、查看表结构用desc
        desc emp;
     
    2、空表dual,最常用的空表,如:
        select 2 * 4 from dual;
        select sysdate from dual;
     
    3、双引号能保持格式
        如:select sysdate “toDay 日 期” from dual;
     
    4、|| 字符串连接
        如:select 2*3 || 8 from dual;
        select ename || sal from scott.emp;
        select ename || ‘ORACLE’ from scott.emp;
     
    5、单引号,如:select 2 * 2 || 'abc''efg' from dual;
        用两个单引号表示一个单引号
     
    6、去掉重复数据distinct
        select distinct deptno from scott.emp;
        去掉重复组合:select distinct deptno,job from scott.emp;
     
    7、where查询
        A、=查询,select * from scott.emp where sal = 1500;
     
        B、比较<、>、>=、<=
            select * from scott.emp where sal > 1500;
        C、and or
            select * from scott.emp where sal > 1500 and sal <= 5000 or deptno = 10;
        D、innot in
            select * from scott.emp where sal in (1500, 800) and deptno not in (10, 20)
     
        E、like模糊 escape 转义
            Select * from scott.emp where ename like ‘%in%’;
            Select * from scott.emp where ename like ‘%in\%k%’;
            Select * from scott.emp where ename like ‘%in#%k%’ escape ‘#’;
            表示like中的#号是转义字符,相当于\
        F、is nullis not null
        K、    order by
            select sal, ename from scott.emp order by sal;
            select sal, ename from scott.emp order by sal asc;
            select sal, ename from scott.emp order by sal desc;
            select sal, ename from scott.emp where sal > 2000 order by sal desc;
            select sal, deptno, ename from scott.emp order by sal,deptno desc;
        
    8、function
        A、lowerupper、substr
            select lower(‘abcABC’) from dual;
            select upper(‘abcABC’) from dual;
            substr(target, startIndex, length)
            select substr(‘abcABC’, 1, 3) from dual;
     
        B、chr、ascii
            将数字安装ascii值转换成字符:select char(65) from dual;
            将字符转换成ascii值:select ascii(‘Z’) from dual;
        
        C、round、to_char
            精确小数
            select round(22.456) from dual;
            保留2位小数:select round(22.456, 2) from dual;
            精确到个位:select round(22.456, -1) from dual;
        
            货币
            设置货币格式,000前面不足就用0代替
            select to_char(sal, '$000,000.00') from scott.emp;
            999就不会替换不足的地方,只会安装格式输出
            select to_char(sal, '$999,999.99') from scott.emp;
            本地货币格式
            select to_char(sal, 'L999,999.99') from scott.emp;
     
            日期
            日期格式 
            格式控制 描述 
            YYYY、YYY、YY 分别代表4位、3位、2位的数字年 
            YEAR 年的拼写 
            MM 数字月 
            MONTH 月的全拼 
            MON 月的缩写 
            DD 数字日 
            DAY 星期的全拼 
            DY 星期的缩写 
            AM 表示上午或者下午 
            HH24、HH12 12小时制或24小时制 
            MI 分钟 
            SS 秒钟 
            SP 数字的拼写 
            TH 数字的序数词 
     
            “特殊字符” 假如特殊字符 
            HH24:MI:SS AM 15:43:20 PM
            select to_char(sysdate, 'YYYY-MM-DD HH:MI:SS') from dual;
            select to_char(sysdate, 'YYYY-MM-DD HH24:MI:SS') from dual;
     
         D、to_date、to_number、nvl
            to_date(target, current_format)
            select to_date('2011-4-2 17:55:55', 'YYYY-MM-DD HH:MI:SS') from dual;
            select to_number('$12,322.56', '$999,999.99') + 10 from dual;
            select to_number('$12,322.56', '$00,000.00') + 10 from dual;
            select to_number('22.56') + 10 from dual;
            nvl可以将某个字段的空值转换成指定的值
            select ename, sal, nvl(comm, 1.00) from scott.emp;
     
    9、group function 组函数:minmaxavgsumcount
            select max(sal) from scott.emp;
            select min(sal) from scott.emp;
            select avg(sal) from emp;
            select round(avg(sal), 2) from emp;
            select to_char(avg(sal), 'L999,999.99') from emp;
            select sum(sal) from emp;
            select count(comm) from emp;
            select count(distinct deptno) from emp;
     
    10、group by 分组
        select deptno, avg(sal) from emp group by deptno;
        select deptno, job, avg(sal) from emp group by deptno, job;
        求部门最高工资的所在部门的员工信息:
        select deptno, ename, sal from emp where sal in (select max(sal) from emp group by deptno);
     
    11、having 对分组数据进行过滤
        求部门评价工资:
        select * from (select avg(sal) sal, deptno from emp group by deptno) where sal > 2000;
        select avg(sal) sal, deptno from emp group by deptno having avg(sal) > 2000;
     
    12、子查询
        求部门分组后工资最高的员工信息
        select emp.ename, emp.sal, emp.deptno from emp, (select max(sal) max_sal, deptno from emp group by deptno) t where emp.sal = t.max_sal and emp.deptno = t.deptno;
        求部门平均工资等级
        select s.grade, t.deptno, t.avg_sal from scott.salgrade s, (select deptno, avg(sal) avg_sal from emp group by deptno) t where t.avg_sal > s.losal and t.avg_sal < s.hisal;(between
     
    13、自连接
        select a.ename, b.ename mgr_name from emp a, emp b where a.empno = b.mgr;
     
    14、 连接查询
        select dname, ename from dept, emp where dept.deptno = emp.deptno;
        select dname, ename from dept join emp on dept.deptno = emp.deptno;
        select dname, ename from dept join emp using(deptno);
        select dname, ename from dept left join emp on dept.deptno = emp.deptno;
        select dname, ename from dept right join emp on dept.deptno = emp.deptno;
        select dname, ename from dept full join emp on dept.deptno = emp.deptno;
        select a.ename, b.ename mgr_name from emp a join emp b on a.mgr = b.empno;
        select a.ename, b.ename mgr_name from emp a left join emp b on a.mgr = b.empno;
     
    15、 Rownum
        select rounum, deptno, dname from dept;
        select * from (
             select rownum r, dept.* from dept
        ) t where  t.r > 2;
     
    16、树状结构查询
        select level, empno, ename, mgr from emp
        connect by prior mgr = empno;
     
    17、排序函数
        --按部门分组,给出分组后的序号
        select row_number() over(partition by deptno order by sal), emp.* from emp;
        
        --rank排序,空出相同部分
        select rank() over(partition by deptno order by sal), emp.* from emp;
        select rank() over(order by deptno), emp.* from emp;
        select rank() over(order by sal), emp.* from emp;
        
        --dense_rank排序给出相同序号,不空留序号
        select rank() over(order by sal), emp.* from emp;
        select dense_rank() over(order by sal), emp.* from emp;
     
    18、交集、并集、割集查询
        --并集:不带重复数据
        select * from emp
        union
        select * from emp2;
        
        --并集:带重复数据
        select * from emp
        union all
        select * from emp2;        
        
        --割集,显示不同部分
        select * from emp
        minus
        select * from emp2;
     
    19、 查询系统表、视图
        select owner, object_name, object_type, status, dba_objects.* from dba_objects where object_type = 'view' and status = 'invalid';
     
        select * from user_objects where object_type like 'PROCEDURE';
     
    20、练习题
        --部门最高薪资员工信息
        select ename, sal, deptno from emp 
        where sal in (select max(sal) from emp group by deptno);
        
        --部门最高薪资员工信息
        select ename, sal, emp.deptno from emp 
        join (select max(sal) max_sal, deptno from emp group by deptno) t 
        on emp.deptno = t.deptno and emp.sal = t.max_sal;
        
        --部门平均薪资等级
        select grade, losal, hisal, t.avg_sal from salgrade 
        join (select avg(sal) avg_sal, deptno from emp group by deptno) t
        on t.avg_sal between losal and hisal;
        
        --经理人
        select ename, job from emp where empno in (select mgr from emp);
        
        --不用分组函数,查询薪水最高值
        select * from (select sal, ename from emp order by sal desc) where rownum = 1;
        select distinct a.sal from emp a join emp b on a.sal > b.sal where rownum = 1;
        select sal from emp where sal not in (select distinct a.sal from emp a join emp b on a.sal < b.sal);
        
        --部门平均薪水最高的部门编号
        select deptno, t.avg_sal from (select avg(sal) avg_sal, deptno from emp group by deptno) t
        where avg_sal = (
            select max(avg_sal) max_sal from (select avg(sal) avg_sal, deptno from emp group by deptno)
        );
        
        select deptno, t.avg_sal from (select avg(sal) avg_sal, deptno from emp group by deptno) t
        where avg_sal = (
            select max(avg(sal)) max_sal from emp group by deptno
        );
        
        --部门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) t
         where avg_sal = (
                select max(avg_sal) max_sal from (select avg(sal) avg_sal, deptno from emp group by deptno)
         )
        );
        
        select dname from dept where deptno = (
            select deptno from (select avg(sal) avg_sal, deptno from emp group by deptno) t
            where avg_sal = (
                   select max(avg(sal)) from emp group by deptno
            )
        );
        
        --平均薪水最低的部门的部门名称
        select dname from dept where deptno = (
          select deptno from (select avg(sal) avg_sal, deptno from emp group by deptno) 
          where avg_sal = (
            select min(avg_sal) min_sal from (
                   select avg(sal) avg_sal from emp group by deptno
            )
          )
        );
        
        select dname from dept where deptno = (
            select deptno from (select avg(sal) avg_sal, deptno from emp group by deptno) 
            where avg_sal = (    
              select min(avg(sal)) avg_sal from emp group by deptno
            )
        );
        
        --平均薪水等级最低的部门的部门名称
        select dname from dept where deptno = (
        select deptno from (
             select grade, t.deptno from salgrade s join (
                select avg(sal) avg_sal, deptno from emp group by deptno
             ) t
             on t.avg_sal between s.losal and s.hisal
          )
          where grade = (
            select min(grade) from salgrade s join (
                select avg(sal) avg_sal, deptno from emp group by deptno
            ) t
            on t.avg_sal between s.losal and s.hisal
          )
        );
        
        --部门经理人中,平均薪水最低的部门名称
        select t.deptno, dname from (
            select sal, deptno from emp where empno in (select distinct mgr from emp)
        ) t join dept 
        on t.deptno = dept.deptno
        where sal = (
            select min(sal) from emp where empno in (select distinct mgr from emp)
        );
        
        --比普通员工的最高薪水还要高的经理人名称
        select * from (
            select empno, ename, sal from emp where empno in (select distinct mgr from emp where mgr is not null)
        ) t
        where t.sal > (
            select max(sal) max_sal from emp where empno not in (
             select distinct mgr from emp where mgr is not null
            )
        );
        
  • 作者:hoojo
    出处:
    blog:http://blog.csdn.net/IBM_hoojo
    本文版权归作者和博客园共有,欢迎转载,但未经作者同意必须保留此段声明,且在文章页面明显位置给出原文连接,否则保留追究法律责任的权利。

版权所有,转载请注明出处 本文出自:
分享道版权所有,欢迎转载,转载请注明出处,谢谢
收藏
关注
评论
查看全文
  • 相关阅读:
    JSP 编码解说
    window系统之mongoDB安装,启动及如何设置为windows服务(总结)
    operator 安装
    JavaScript学习2
    JavaScript学习3
    win7的便签很好使
    COM技术内幕第九章笔记编程工作的简化
    VS乱码之UTF8篇
    必须而不是推荐尽量使用const引用参数
    查看不到网络连接(可以上网)
  • 原文地址:https://www.cnblogs.com/hoojo/p/2035246.html
  • Copyright © 2011-2022 走看看