Oracle(day3)数据表的连接

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　　上节回顾：
1、order by 子句
order by + 字段名，字段名,字段名...
order by + list列表值，list列表值,list列表值...
　　2、where 子句
算术运算符
SQL运算符
逻辑运算符
　　3、单行函数
　　
作业内容：
1、对员工表中日期值进行排序。
select to_char(start_date,'yyyy-mm-dd')Time from s_emp order by start_date desc;
　　
Oracle day3
查询连接
　　
等值连接
查询员工表员部门编号为41的员工姓名；
select frist_name || last_name "姓名" from s_emp where dept_id=41;
　　查询员工表员姓名为LaDorisNgao的员工信息；
select * from s_emp where first_name = 'LaDoris';
　　
非等值连接
查询员工表中部门编号在40到42之间的所有员工信息；
select * from s_emp where dept_id between 40 and 42;
　　
查询员工表中员工编号为1,5,9,23的员信息;
select * from s_emp where id in(1,5,9,23);
　　
外连接
左外连接
select s_a.last_name "A NAME",s_b.last_name "B NAME" from s_emp s_a ,s_emp s_b where s_a.id= s_b.manager_id(+);
　　select s_a.last_name,s_b.last_name from s_emp s_a left outer join s_emp s_b on s_a.id = s_b.manager_id;
　　右外连接
select s_a.last_name,s_b.last_name from s_emp s_a ,s_emp s_b where s_a.id(+)= s_b.manager_id;
　　select s_a.last_name,s_b.last_name from s_emp s_a right outer join s_emp s_b on s_a.id = s_manager_id;
　　from 第一表(A)，第二表(B)
A B
　　左：B===》A======》只要跟A表内容相匹配，A表内容都显示，B表内容补空
右：A===》B ======》只要跟B表内容相匹配，B表内容都显示, A表内容补空
　　
自连接(A表和B表代表同一张表)
select s_a.last_name,s_b.last_name from s_emp s_a ,s_emp s_b where s_a.id= s_b.manager_id;
　　
oracle 10g
　　笛卡尔积
交叉连接
select s_a.last_name,s_b.last_name from s_emp s_a ,s_emp s_b;
　　
　　
　　组函数
AVG (DISTINCT|ALL|n)平均值
COUNT (DISTINCT|ALL|expr|*)统计个数
MAX (DISTINCT|ALL|expr)最大值
MIN (DISTINCT|ALL|expr)最小值
SUM (DISTINCT|ALL|n)求和
　　
select avg(salary),count(salary),max(salary),min(salary),sum(salary) from s_emp;
　　
查询员工表中姓名的最大值和最小值
SELECTMIN(last_name), MAX(last_name) FROMs_emp;
　　
　　Group by ........Having
SELECT字段名 FROM 表名[ where 条件 GROUP BY 分组条件 having(过滤条件) ORDER BY 字段名]
　　
　　按部门编号分组统计员工表中工资；
select sum(salary) from s_emp group by dept_id;
　　查询部门表中对部门名字进行统计
SELECTregion_id, COUNT(name) FROMs_dept; 报错
SELECTregion_id, COUNT(name) FROMs_dept group by region_id order by region_id;
　　
查询员工表中按部门编号分组在按标题分组；
SELECTdept_id, title,salary, COUNT(*) FROMs_emp GROUP BYdept_id, title ,salary;
　　
group by 字段名,字段名,字段名.....
　　查询员工表中对部门编号做统计
SELECTdept_id , count(*) FROMs_emp GROUP BY dept_id order by dept_id;
查询员工表中部门编号统计大于2的记录
SELECTdept_id , count(*) FROMs_emp GROUP BY dept_id having count(*)>2;
　　查询员工表中标题数量大于5的记录
select title , 12*avg(salary), count(*) from s_emp group by title having count(*)>5;
　　
select title ,avg(salary) from s_emp where title not like'%Stock%' group by title having avg(salary) > 1000;
　　
　　子查询
　　查出所有员工低于平均工资的记录
　　select avg(salary) from s_emp;
　　select * from s_emp where salary < 平均工资
　　select * from s_emp where salary < (select avg(salary) from s_emp);
　　
　　查询一个名字叫Biri的同一个部门的员工
select dept_id from s_emp where last_name = 'Biri';
　　select * from s_emp where dept_id = 部门ID
　　select * from s_emp where dept_id = (select dept_id from s_emp where last_name = 'Biri');
　　
语法结构：
SELECTselect_list
FROMtable
WHEREexpr operator
(SELECTselect_list
FROMtable where (select ......));