创建数据库

CREATE DATABASE IF NOT EXISTS database_name;

查看所有数据库

show databases

删除数据库

DROP DATABASE IF EXISTS sample_database;

进入数据库

use dbname

 

创建表

CREATE TABLE IF NOT EXISTS test.student

(name STRING, age INT, contact INT );

查看所有表

show tables

 

/指定HDFS路径建库

为了在HDFS文件系统中创建数据库，需要指定要创建数据库的位置，如下所示。

CREATE DATABASE IF NOT EXISTS database_name LOCATION hdfs_path;

实测会报无权限

CREATE DATABASE IF NOT EXISTS hdfstest LOCATION "/db/hdfstest";

改个有权限的目录即可：

CREATE DATABASE IF NOT EXISTS hdfstest LOCATION "/user/impala/db/hdfstest";

注：通过hadoop fs -ls /user类似命令找到有权限的目录

建表后会在hdfs数据库目录下创建表的目录

插入数据后数据会存在表目录中。

 

insert

create table employee (Id INT, name STRING, age INT,address STRING, salary BIGINT);

insert into employee (ID,NAME,AGE,ADDRESS,SALARY)VALUES (1, 'Ramesh', 32, 'Ahmedabad', 20000 );

///查询

select * from employee

排序

select id,name,age,address,salary from employee order by id

select * from employee order by salary desc nulls last

 

select * from table_name ORDER BY col_name [ASC|DESC] [NULLS FIRST|NULLS LAST]

可以使用关键字ASC或DESC分别按升序或降序排列表中的数据。

以同样的方式，如果我们使用NULLS FIRST，表中的所有空值都排列在顶行; 如果我们使用NULLS LAST，包含空值的行将最后排列。

 

分组查询

select name,sum(salary) from employee group by name

select name,sum(salary) from employee group by name having sum(salary)>20000

翻页查询

select * from employee order by id limit 2 offset 2

 

///union

select * from employee order by id limit 2

union

select * from employee order by id limit 4

 

select * from employee order by id limit 2

union all

select * from employee order by id limit 4

 

with

with x as (select 1), y as (select 2) (select * from x union y);

 

with t1 as (select * from employee where age>30),

t2 as (select * from employee where age>25)

(select * from t1 union all select * from t2);

 

distinct

select distinct id,name from employee;

 

/覆盖插入（表的所有数据都被删除）

Insert overwrite employee values (1, 'Ram', 26,  

'Vishakhapatnam', 37000 ) 

 

///获取表的描述（表结构）

describe employee

 

改表名

ALTER TABLE [old_db_name.]old_table_name RENAME TO [new_db_name.]new_table_name

ALTER TABLE hdfstest.employee RENAME TO hdfstest.users;

 

/添加列

ALTER TABLE users ADD COLUMNS (account_no BIGINT, phone_no BIGINT);

删除列

ALTER TABLE users DROP account_no;

/更改列名和类型

ALTER TABLE users CHANGE phone_no e_mail string;

删除表

drop table if exists my_db.student;

///清空表

truncate table_name;

 

 

创建视图

CREATE VIEW IF NOT EXISTS users_view AS

select name, age from users;

/修改视图

alter view users_view AS

select name, age,e_mail from users;

//删除视图

drop view users_view

 

参考链接：https://www.w3cschool.cn/impala/