2014-04-07
1.查询每个员工对应的部门
SQL>conn hr/hr;
##查询表
SQL>select object_name from user_objects where object_type='TABLE';
##查看两张表结构
SQL>desc employees;
SQL>desc departments;
##关联查询
SQL>select a.first_name || ' ' ||a.last_name name,employee_id,b.department_name from employees a join departments b on a.department_id=b.department_id;
2.连接
等值连接：inner join
左连接：left join
右连接：right join
自连接：self join
3.查询员工对应的部门和城市
##查询表
SQL>select object_name from user_objects where object_type='TABLE';
##查看三张表结构
SQL>desc employees;
SQL>desc departments;
HR@orcl> desc locations;
##关联查询
HR@orcl> select a.employee_id,a.department_id,c.city from employees a join departments b on a.department_id=b.department_id join locations c on b.location_id=c.location_id;
##将SQL缓冲区内容保存到文件中
HR@orcl> save 1.sql;
HR@orcl> !
##编辑配置文件
[oracle@oracle53 ~]$ vim 1.sql
==================================
rem query employee_id,employee_name,department_id,city
set linesize 500;
col name for a20;
col city for a30;
select a.employee_id,a.first_name || ' ' ||a.last_name name,a.department_id,c.cii
ty from employees a join departments b on a.department_id=b.department_id join ll
ocations c on b.location_id=c.location_id
/
====================================
[oracle@oracle53 ~]$ exit
4.所有员工对应的部门
//left [outer] join:不仅会返回满足连接条件（等值连接）的所有记录，而且还会返回不满足条件的连接操作符左边表的其他行。
HR@orcl 14:04:07-09:57:55> select a.employee_id,a.last_name ||' '||a.first_name name,b.department_name from employees a left join departments b on a.department_id=b.department_id;
##传统用例：把（+）放在行数较少的一端，只能用于左右连接
HR@orcl 14:04:07-10:34:56> select a.employee_id,a.last_name ||' '||a.first_name name,b.department_name from employees a,departments b where a.department_id=b.department_id(+);
5.所有部门对应的员工
//right [outer] join:不仅会返回满足连接条件（等值连接）的所有记录，而且还会返回不满足条件的连接操作符右边表的其他行。
select a.employee_id,a.last_name ||' '||a.first_name name,b.department_name from employees a right join departments b on a.department_id=b.department_id;
##传统用例
HR@orcl> select a.employee_id,a.last_name ||' '||a.first_name name,b.department_name from employees a,departments b where a.department_id(+)=b.department_id;
6.查询员工对应的上司
HR@orcl> select a.employee_id,a.last_name ||' '||a.first_name name,b.employee_id,b.last_name||' '||b.first_name mname from employees a join employees b on a.manager_id=b.employee_id;
7.全连接
HR@orcl> select a.employee_id,a.last_name||' '||a.first_name name,b.department_name from employees a full join departments b on a.department_id=b.department_id;
8.数据分组
组函数又称为多行函数，把多行当作一个整体进行处理。
avg(),sum(),max(),min(),distinct(),group by,having
having:用来限制分组显示结果
group by:对查询结果进行分组统计
9.组函数使用原则：
1）distinct表示值不重复；
2）所有组函数忽略空值，为了用一个值代替空值，用nvl,nvl2,coalesce函数；
----重点强调--------
3）使用group by来分组时，oracle服务器隐式以升序排序结果集
##统计每个部门的平均工资
HR@orcl> select department_id,round(avg(salary),2) from employees group by department_id;
##统计每个部门的最小工资，最大工资
HR@orcl> select department_id,min(salary),max(salary) from employees group by department_id;
##统计每个部门有多少员工
HR@orcl> select department_id,count(employee_id) from employees group by department_id;
##统计每个部门的绩效 ---先处理空值，再求平均值
HR@orcl 14:04:07-11:28:03> select department_id,avg(nvl(commission_pct,0)) from employees group by department_id;
------having--------
sql>select department_id,avg(nvl(commission_pct,0)) from employees group by department_id having avg(nvl(commission_pct,0))>0.2;
10.子查询
子查询是指嵌入在其他的SQL语句中的SELECT语句，也称为嵌套查询。
//单行子查询结果只返回一行，如果用等于只能用单行子查询
##雇员编号为141工作类型，查询所有从事这个工作类型的雇员
SQL> select last_name|| ' '||first_name employee_name,job_id from employees where job_id= (select job_id from employees where employee_id=141);
//多行子查询
SQL> select last_name|| ' '||first_name employee_name,job_id from employees where job_id in (select job_id from employees in employee_id (141,142));
in:等于列表中的任何成员
any:比较子查询返回的每个值
all：比较子查询返回的全部值
SQL> select employee_id,last_name,salary from employees where salary < any (select salary from employees where job_id='IT_PROG') and job_id !='IT_PROG';
SQL> select employee_id,last_name,salary from employees where salary < all (select salary from employees where job_id='IT_PROG') and job_id !='IT_PROG';
11.行记录标识
rownum:行记录在表中的逻辑地址
rowid：行记录在表中的物理地址，十个字节
SQL> select employee_id,last_name,salary,rownum,rowid from employees where salary < all (select salary from employees where job_id='IT_PROG') and job_id !='IT_PROG';
EMPLOYEE_ID LAST_NAME SALARY ROWNUM ROWID
----------- ------------------------- ---------- ---------- ------------------
185 Bull 4100 1 AAAR5pAAFAAAADPABV
192 Bell 4000 2 AAAR5pAAFAAAADPABc
193 Everett 3900 3 AAAR5pAAFAAAADPABd
12.数据类型
//字符类型：char(),varchar2(),colb,blob,bfile
varcha2()可变，数据库字符集
//数值类型:number()----oracle 9i数据库引擎支持的
binary_integer,binary_float,binary_double
//时间类型：date.timestamp
HR@orcl 14:04:07-03:25:18> create table d(d timestamp);
HR@orcl 14:04:07-03:25:47> insert into d values(sysdate);
HR@orcl 14:04:07-03:26:42> select * from d;
-----------------------------------------------------------
07-APR-14 03.26.42.000000 PM ---默认精度为6位
-----------------------------------------------------------
//扩展：
oracle：移动表空间中的数据文件
alter tablespace tbs_01 offline; -----脱机表空间
host mv /tmp/datafile1.dbf /tmp/tbs/datafile1.dbf -----移动数据文件
alter tablespace tbs_01 rename datafile '/tmp/datafile1.dbf' to '/tmp/tbs/datafile1.dbf' -----对数据文件进行重命名，也就时告知数据库数据文件的位置
select a.ts#,a.name,b.name from v$tablespace a join v$datafile b on a.ts#=b.ts#; -----查询表空间与数据文件的对应
alter tablespace tbs_01 online; ------重新联机
///
语法：SELECT 语句1 [UNION|UNION ALL|INTERSECT|MINUS] SELECT 语句2
UNION
UNION操作符用于获取两个结果集的并集。当使用该操作符时，会自动出掉结果集中的重复行，并且会以第一列的结果进行排序。
SELECT ENAME,SAL,JOB FROM EMP WHERE SAL > 2500
union
SELECT ENAME,SAL,JOB FROM EMP WHERE JOB='MANAGER';
UNION ALL
UNION ALL操作符用于获取两个结果集的并集，但与UNION操作符不同，该操作符不会取消重复值，而且也不会以任何列进行排序。
SELECT ENAME,SAL,JOB FROM EMP WHERE SAL > 2500
UNION ALL
SELECT ENAME,SAL,JOB FROM EMP WHERE JOB='MANAGER';
INTERSECT
INTERSECT操作符用于获取两个结果集的交集，当使用该操作符时，只会显示同时存在于两个结果集中的数据，并且会以第一列进行排序。
SELECT ENAME,SAL,JOB FROM EMP WHERE SAL > 2500
INTERSECT
SELECT ENAME,SAL,JOB FROM EMP WHERE JOB='MANAGER';
MINUS
把集合{x∣x∈A,且x∉B}叫做A与B的差集，记作A－B
MINUS操作符用于获取两个结果集的差集，当使用该操作符时，只会显示在第一个结果集中存在，在第二个结果集中不存在的数据，并且会以第一列进行排序。
SELECT ENAME,SAL,JOB FROM EMP WHERE SAL > 2500
MINUS
SELECT ENAME,SAL,JOB FROM EMP WHERE JOB='MANAGER';
来源：oschina
链接：https://my.oschina.net/u/1442209/blog/221181