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目录
数据准备：
1，创建emp表和dept表，并向其中导入如下的数据：
create database db_select;
use db_select;
create table if not exists dept(
deptno int,
dname string,
loc int
)
row format delimited
fields terminated by '\t';
create table if not exists emp(
empno int,
ename string,
job string,
mgr int,
hiredata string,
sal double,
comm double,
deptno int
)
row format delimited
fields delimited by '\t';
0: jdbc:hive2://hadoop108:10000> show tables;
+-----------+--+
| tab_name |
+-----------+--+
| dept |
| emp |
| location |
+-----------+--+
[isea@hadoop108 datas]$ vim dept.txt
10 ACCOUNTING 1700
20 RESEARCH 1800
30 SALES 1900
40 OPERATIONS 1700
[isea@hadoop108 datas]$ vim emp.txt
7369 SMITH CLERK 7902 1980-12-17 800.00 20
7499 ALLEN SALESMAN 7698 1981-2-20 1600.00 300.00 30
7521 WARD SALESMAN 7698 1981-2-22 1250.00 500.00 30
7566 JONES MANAGER 7839 1981-4-2 2975.00 20
7654 MARTIN SALESMAN 7698 1981-9-28 1250.00 1400.00 30
7698 BLAKE MANAGER 7839 1981-5-1 2850.00 30
7782 CLARK MANAGER 7839 1981-6-9 2450.00 10
7788 SCOTT ANALYST 7566 1987-4-19 3000.00 20
7839 KING PRESIDENT 1981-11-17 5000.00 10
7844 TURNER SALESMAN 7698 1981-9-8 1500.00 0.00 30
7876 ADAMS CLERK 7788 1987-5-23 1100.00 20
7900 JAMES CLERK 7698 1981-12-3 950.00 30
7902 FORD ANALYST 7566 1981-12-3 3000.00 20
7934 MILLER CLERK 7782 1982-1-23 1300.00 10
[isea@hadoop108 datas]$ vim location.txt
1700 Beijing
1800 London
1900 Tokyo
load data local inpath '/opt/module/datas/dept.txt' into table dept;
load data local inpath '/opt/module/datas/emp.txt' into table emp;
load data local inpath '/opt/module/datas/location.txt' into table location;分组实操练习：
1，计算每个部门的平均工资：
select deptno,avg(sal) from emp group by deptno;
+---------+---------------------+--+
| deptno | _c1 |
+---------+---------------------+--+
| 10 | 2916.6666666666665 |
| 20 | 2175.0 |
| 30 | 1566.6666666666667 |
+---------+---------------------+--+
2，计算emp每个部门的最高薪水：
select deptno,max(sal) from emp group by deptno;
+---------+---------+--+
| deptno | _c1 |
+---------+---------+--+
| 10 | 5000.0 |
| 20 | 3000.0 |
| 30 | 2850.0 |
+---------+---------+--+
3，求每个部门的平均薪水大于2000的部门：
select deptno,avg(sal) AVG from emp group by deptno having AVG > 2000;
+---------+---------------------+--+
| deptno | avg |
+---------+---------------------+--+
| 10 | 2916.6666666666665 |
| 20 | 2175.0 |
+---------+---------------------+--+
4，根据员工表和部门表中的部门编号相等，查询员工编号、员工名称和部门名称；
select empno,ename,dname from emp left join dept on emp.deptno = dept.deptno;
+--------+---------+-------------+--+
| empno | ename | dname |
+--------+---------+-------------+--+
| 7369 | SMITH | RESEARCH |
| 7499 | ALLEN | SALES |
| 7521 | WARD | SALES |
| 7566 | JONES | RESEARCH |
| 7654 | MARTIN | SALES |
| 7698 | BLAKE | SALES |
| 7782 | CLARK | ACCOUNTING |
| 7788 | SCOTT | RESEARCH |
| 7839 | KING | ACCOUNTING |
| 7844 | TURNER | SALES |
| 7876 | ADAMS | RESEARCH |
| 7900 | JAMES | SALES |
| 7902 | FORD | RESEARCH |
| 7934 | MILLER | ACCOUNTING |
+--------+---------+-------------+--+
Join连接实操练习：
合并员工表和部门表：这里使用到了内连接
select e.ename,e.empno,e.sal,e.deptno,d.dname from emp e join dept d on e.deptno = d.deptno;
+----------+----------+---------+-----------+-------------+--+
| e.ename | e.empno | e.sal | e.deptno | d.dname |
+----------+----------+---------+-----------+-------------+--+
| SMITH | 7369 | 800.0 | 20 | RESEARCH |
| ALLEN | 7499 | 1600.0 | 30 | SALES |
| WARD | 7521 | 1250.0 | 30 | SALES |
| JONES | 7566 | 2975.0 | 20 | RESEARCH |
| MARTIN | 7654 | 1250.0 | 30 | SALES |
| BLAKE | 7698 | 2850.0 | 30 | SALES |
| CLARK | 7782 | 2450.0 | 10 | ACCOUNTING |
| SCOTT | 7788 | 3000.0 | 20 | RESEARCH |
| KING | 7839 | 5000.0 | 10 | ACCOUNTING |
| TURNER | 7844 | 1500.0 | 30 | SALES |
| ADAMS | 7876 | 1100.0 | 20 | RESEARCH |
| JAMES | 7900 | 950.0 | 30 | SALES |
| FORD | 7902 | 3000.0 | 20 | RESEARCH |
| MILLER | 7934 | 1300.0 | 10 | ACCOUNTING |
+----------+----------+---------+-----------+-------------+--+
这里如果没一个员工刚来，暂时没有分配部门，将不会显示在查询结果中
左外连接：左表的所有记录都会被保留下来，没有匹配到的，以null显示:
select e.empno,e.ename,e.sal,d.dname from emp e left join dept d where e.deptno = d.deptno;
+----------+----------+---------+-------------+--+
| e.empno | e.ename | e.sal | d.dname |
+----------+----------+---------+-------------+--+
| 7369 | SMITH | 800.0 | RESEARCH |
| 7499 | ALLEN | 1600.0 | SALES |
| 7521 | WARD | 1250.0 | SALES |
| 7566 | JONES | 2975.0 | RESEARCH |
| 7654 | MARTIN | 1250.0 | SALES |
| 7698 | BLAKE | 2850.0 | SALES |
| 7782 | CLARK | 2450.0 | ACCOUNTING |
| 7788 | SCOTT | 3000.0 | RESEARCH |
| 7839 | KING | 5000.0 | ACCOUNTING |
| 7844 | TURNER | 1500.0 | SALES |
| 7876 | ADAMS | 1100.0 | RESEARCH |
| 7900 | JAMES | 950.0 | SALES |
| 7902 | FORD | 3000.0 | RESEARCH |
| 7934 | MILLER | 1300.0 | ACCOUNTING |
+----------+----------+---------+-------------+--+
这里如果没一个员工刚来，暂时没有分配部门，也会显示在查询结果中
右外连接：右表的所有记录都会被保留下来，没有匹配到的，以null显示：
select e.empno,e.ename,e.sal,d.dname from emp e right join dept d where e.deptno = d.deptno;
+----------+----------+---------+-------------+--+
| e.empno | e.ename | e.sal | d.dname |
+----------+----------+---------+-------------+--+
| 7782 | CLARK | 2450.0 | ACCOUNTING |
| 7839 | KING | 5000.0 | ACCOUNTING |
| 7934 | MILLER | 1300.0 | ACCOUNTING |
| 7369 | SMITH | 800.0 | RESEARCH |
| 7566 | JONES | 2975.0 | RESEARCH |
| 7788 | SCOTT | 3000.0 | RESEARCH |
| 7876 | ADAMS | 1100.0 | RESEARCH |
| 7902 | FORD | 3000.0 | RESEARCH |
| 7499 | ALLEN | 1600.0 | SALES |
| 7521 | WARD | 1250.0 | SALES |
| 7654 | MARTIN | 1250.0 | SALES |
| 7698 | BLAKE | 2850.0 | SALES |
| 7844 | TURNER | 1500.0 | SALES |
| 7900 | JAMES | 950.0 | SALES |
+----------+----------+---------+-------------+--+
这里如果有一个刚陈成立的部门，暂时没有员工被调到该部门，那么这个部门仍然会显示在这个部门中
满外连接：左右表中的，没有匹配到的，都会以null显示
select e.empno,e.ename,e.sal,d.dname from emp e full join dept d where e.deptno = d.deptno;
+----------+----------+---------+-------------+--+
| e.empno | e.ename | e.sal | d.dname |
+----------+----------+---------+-------------+--+
| 7934 | MILLER | 1300.0 | ACCOUNTING |
| 7839 | KING | 5000.0 | ACCOUNTING |
| 7782 | CLARK | 2450.0 | ACCOUNTING |
| 7876 | ADAMS | 1100.0 | RESEARCH |
| 7788 | SCOTT | 3000.0 | RESEARCH |
| 7369 | SMITH | 800.0 | RESEARCH |
| 7566 | JONES | 2975.0 | RESEARCH |
| 7902 | FORD | 3000.0 | RESEARCH |
| 7844 | TURNER | 1500.0 | SALES |
| 7499 | ALLEN | 1600.0 | SALES |
| 7698 | BLAKE | 2850.0 | SALES |
| 7654 | MARTIN | 1250.0 | SALES |
| 7521 | WARD | 1250.0 | SALES |
| 7900 | JAMES | 950.0 | SALES |
+----------+----------+---------+-------------+--+
没有部门的员工和没有员工的部门都会显示在这张表中多表的连接实操练习：
1,多表的连接查询：
select e.ename,d.dname,l.loc_name
from emp e left join dept d on e.deptno = d.deptno
left join location l on
d.loc = l.loc;
+----------+-------------+-------------+--+
| e.ename | d.dname | l.loc_name |
+----------+-------------+-------------+--+
| SMITH | RESEARCH | London |
| ALLEN | SALES | Tokyo |
| WARD | SALES | Tokyo |
| JONES | RESEARCH | London |
| MARTIN | SALES | Tokyo |
| BLAKE | SALES | Tokyo |
| CLARK | ACCOUNTING | Beijing |
| SCOTT | RESEARCH | London |
| KING | ACCOUNTING | Beijing |
| TURNER | SALES | Tokyo |
| ADAMS | RESEARCH | London |
| JAMES | SALES | Tokyo |
| FORD | RESEARCH | London |
| MILLER | ACCOUNTING | Beijing |
+----------+-------------+-------------+--+
大多数情况下，Hive会对每对JOIN连接对象启动一个MapReduce任务。本例中会首先启动一个MapReduce job对
表e和表d进行连接操作，然后会再启动一个MapReduce job将第一个MapReduce job的输出和表l;进行连接操作